John Bolton (search) strode past reporters Tuesday as he traveled up to the 38th floor of his new office building to present his credentials to U.N. Secretary-General Kofi Annan.

The presentation occurred hours after the new U.S. ambassador to the United Nations showed up for his first full day of work in his new role. On Monday, he spent about five hours with U.S. staff at the world body, preparing for his tenure there.

"Glad to be here," Bolton told Annan before handing over his letter of appointment.

The two exchanged greetings and then held a brief private meeting. Bolton entered and left U.N. headquarters smiling and waving, but staying mum. He then went back to work preparing for September's massive U.N. reform summit, for which his staff has been planning for months.

The ambassador was appointed by President Bush on Monday after months of stalling an up-or-down vote on the nomination by a group of senators.

Many Democrats, and at least one Republican — Sen. George Voinovich (search) of Ohio — argued that Bolton was not the best man for the job and accused the administration of stonewalling when the senators asked for certain information regarding Bolton's time as chief adviser to the Secretary of State.

The Bush administration says a tough-talking Bolton is ideally suited to lead an effort to overhaul the U.N. bureaucracy and make it more accountable. But Annan cautioned that negotiation and compromise are the key to success at the United Nations.

"I think it is all right for one ambassador to come and push, but an ambassador always has to remember that there are 190 others who will have to be convinced, or a vast majority of them, for action to take place," Annan said Monday.

Amb. Dennis Ross, former Mideast envoy and FOX News foreign affairs analyst, said the political fight over Bolton is a Washington story, for the most part, and should have little bearing at the United Nations.

"Certainly, people there will be curious about him … it's certainly in his interest to be effective,' Ross said, throwing his support behind Bolton and his mission.

"I think he may surprise people. He's going to be representing the president. What he's going to say is what the president and the secretary [of state] want him to say. He's not going to be a free agent up there," Ross said. Even at the State Department, Ross added, Bolton was "very representative of what the secretary and the president wanted," but there may be more of a focus now on diplomacy.

Dodd: 'Let Him Do His Work'

Even the most critical opponents of Bolton agree that now that the ambassador is formally situated at the United Nations (search), he needs to be able to get some work done on issues such as Iraq, Iran and U.N. reform.

"We've got a very busy agenda at the U.N., it's going to be very difficult to get the job done," Sen. Christopher Dodd (search) told FOX News on Tuesday. "Let's get behind him, let him do his work … I certainly want to see him succeed but I'm going to watch him carefully."

The Connecticut Democrat on Monday blasted the Bush's recess appointment and earlier told FOX News that Bolton was "damaged goods."

The political fighting over Bolton is "going to make it more difficult, in my view, for him to build a consensus at the U.N., but I hope he can succeed. This is over with at this point, let's get the job done," Dodd said Tuesday.

Sen. George Allen (search), R-Va., urged all senators to support the president's pick and put an end to the Bolton-bashing.

"The worst abuse of process is that the United States senators — the majority of which were for John Bolton — were denied the opportunity to have the fairness of an up or down vote," Allen told FOX News. "What they ought to be doing, instead of diminishing and criticizing John Bolton, they ought to get behind him."

He added, "John Bolton is representing the values of the people of the United States and they ought to get over the fact President Bush had to appoint him" to get over what Allen called "obstruction" in the Senate.

Bolton's chief challenge as he tries to advance Bush's reform agenda will be to work with diplomats from 190 nations in a place he's previously described as irrelevant.

The 56-year-old arms control expert with a reputation for brilliance, obstinacy and speaking his mind will arrive at the United Nations (search) just weeks before a summit at which world leaders will seek to adopt sweeping changes to enable the world body to meet the challenges of the 21st century.

Bolton will be thrust into intense negotiations on contentious issues ranging from Security Council reform and poverty alleviation to stepping up the global fight against terrorism and improving U.N. management.

"He will be one of the key players because the United States is the largest contributor and a great power in the Security Council," Germany's U.N. Ambassador Gunter Pleuger said. "There are conflicting views on nearly every issue that is on our plate for the reform, and the largest player in the U.N., of course, plays a key role."

Many U.N. diplomats say Bolton will be judged on his performance there, not on his past, which features sharp criticism of the organization and senate resistance to his appointment as U.S. ambassador.

"No one should make prejudgments on reputation," said Chile's U.N. Ambassador Heraldo Munoz. "One must do it on the merit of the facts, when we see what happens here."

The fact that Bolton failed twice to win Senate confirmation forcing Bush to appoint him Monday after Congress adjourned for the summer, was also unlikely to have an impact, diplomats said.

"He's a colleague like any other and will be received as such," said Denmark's U.N. Ambassador Ellen Margrethe Loj, who noted that in many countries no confirmation of ambassadors is required.

Time to Get Personal

New Mexico Gov. Bill Richardson (search), a former ambassador to the United Nations, said Bolton may face some "stormy" weather at the world body at first but with a little personal attention to the other ambassadors and a demonstration of interest and expertise in how the organization operates, the seas will calm. Being more congenial with U.S. lawmakers won't hurt, either, he said.

"Find a way to make up with some of the senators who opposed him, because senators hold the purse strings" Richardson told FOX News, noting that if Bolton wants to do anything on peacekeeping or other U.N. issues that require U.S. funding, it will have to go through the congressional appropriations process.

Having a close, personal relationship with the Secretary-General himself is also "crucial," Richardson said.

Although Bolton will have a lot of advantages at the building on the East River in New York because he's the American president's personal pick for the post, "he starts out with a lot of question marks," Richardson said.

Of top priority should be an effort to get rid of the bill on Capitol Hill that ties U.S. funding for the United Nations with real reform at the world body, Richardson said.

"Bolton and the president have to kill that measure," he said. "It's going to be critically important if Bolton has some success at the U.N. for him to persuade the Senate and the House that that's not good for the U.S. — it ties your hands at the U.N."

Bolton will certainly face antagonism from some countries including North Korea and Iran. In 2003, the then-undersecretary at the State Department said North Korea was led by a "tyrannical dictator." He also contends Iran is secretly planning to build nuclear weapons.

Bolton has also made comments about the United Nations that may linger in the minds of some.

In 1994, Bolton said it wouldn't make a "bit of difference" if the top 10 floors of the United Nations — which include the Secretary-General's office — vanished from the 39-story headquarters building.

In the same speech, he said there is "no such thing as the United Nations," just "an international community that occasionally can be led by the only real power left in the world, and that is the United States."

But Bolton is no stranger to the U.N.'s inner workings. He dealt with U.N. affairs in the State Department from 1989-93, and in his latest post as the department's arms control chief, he had frequent contacts with the Chinese and Russians, and will find several familiar faces in their delegations and elsewhere.

"Honestly, I'm looking forward to working with him," said Algeria's U.N. Ambassador Abdallah Baali, whose two-year term on the Security Council ends in December. "I worked with him several years ago, and I enjoyed working with him."

"He's a very smart guy who can be very constructive, who can be very creative. So I think it will be very interesting to spend a few months with him in the Security Council," Baali added.

Russia's deputy U.N. Ambassador Konstantin Dolgov said Bolton was well-known in Moscow and "as far as I know he is a negotiator with quite some background."

Diplomats said Bolton's first test will come very quickly in whether he plays a positive role in helping make the September summit a success.

With just over six weeks left to produce a final document that all 191 U.N. member states support, negotiations are heating up on many contentious issues: expanding the Security Council, creating a new Peacebuilding Commission, revamping the U.N.'s human rights machinery, defining terrorism, protecting civilians facing war crimes and genocide, and overhauling the U.N. Secretariat.

"I think this is a time when it is make or break as far as the future relevance of the United Nations is concerned," said Germany's Pleuger.

FOXNews.com's Liza Porteus and The Associated Press contributed to this report.