President Bush is expected to nominate Undersecretary of State John Bolton (search) to be ambassador to the United Nations, but his Senate confirmation may not go as smoothly as the president would like.

Secretary of State Condoleezza Rice announced Monday Bush's intention to nominate Bolton to be the lead diplomat to the United Nations (search).

"President Bush and I have chosen John because he knows how to get things done. He's a tough-minded diplomat, he has a strong history of success and he has a proven track record of effective multilateralism," Rice said in the Ben Franklin Room of the State Department.

"John Bolton is personally committed to the future success of the United Nations and he will be a strong voice for reform at a time when the U.N. has begun to reform itself to help meet the challenging agenda before the international community," Rice said.

If confirmed by the Senate, Bolton will succeed former Sen. John Danforth (search), who retired in January after just six months on the job. Anne Patterson, a career diplomat, has been temporarily filling the spot.

"Madame Secretary, I want to thank you and the president for your confidence and support," Bolton said. "I will continue to work closely with members of Congress as well as with our colleagues in the foreign service and the civil service to advance President Bush's agenda."

Bolton's appointment marks the placement of a conservative on security matters and proliferation issues into a body that clashed famously with the Bush administration on the disarmament of Saddam Hussein in Iraq.

Some Senate Democrats expressed dismay at the president's decision. Senate Democratic Leader Harry Reid (search ) called Bolton "a disappointing choice and one that sends all the wrong signals.

"At a time when President Bush has recognized we need to begin repairing our damaged relations with the rest of the world, he nominates someone with a long history of being opposed to working cooperatively with other nations," Reid said.

Sen. Jon Corzine, D-N.J., also voiced his displeasure.

"[Bolton] is responsible as much as any member of the administration for the needless confrontations with the rest of the world and for the international isolation that plagued President Bush's first term," Corzine said. "Now, when bridge-building and strengthening of alliances are so critical to our national security, he is a poor person to serve as a conciliator at the United Nations."

Corzine is a member of the Senate Foreign Relations Committee, which will hold the confirmation hearings.

A senior Bush administration official said he expected a "messy" confirmation hearing for Bolton. The official intimated, however, that the hard-nosed negotiator could play a critical role if the issue of Iran's nuclear aspirations is referred to the U.N. Security Council.

Bush has allowed Europe to take the lead in negotiating with Iran, and the aide said he'd be "flabbergasted" if the Europeans could win concessions from Tehran.

"That process must break down and be seen to break down" before Bolton, if confirmed, is to use the Security Council as a lever on Tehran, the official said.

The Security Council could consider a resolution listing consequences if Tehran continues to obstruct the probe into its nuclear weapons program.

In remarks after Rice's introduction, Bolton said that "the security of our country and all freedom-loving peoples must be protected," and the United Nations affords the United States the opportunity to move forward with other nations with a unity of purpose.

Administration aides said Bolton, the undersecretary of state for arms control and international security, will work to "build a broader base of support in the United States for the U.N."

Bolton, 56, and an attorney, drew considerable attention to himself for remarks he made denouncing North Korea (search) for its nuclear weapons program. In return, Pyongyang refused to negotiate with him and Bolton was removed from the delegation that had been representing the United States in now-stalled six-party talks.

He also led the American withdrawal from numerous international accords, including the Anti-Ballistic Missile Treaty (search) and the Comprehensive Test Ban Treaty (search). Bolton is also credited with coordinating the U.S. position during negotiations with Libya when it gave up its pursuit of weapons of mass destruction.

Bolton has been in his post since May 2001 but has also held a variety of high-level government jobs at the departments of justice and state under Republican administrations, including assistant secretary of state for President George H.W. Bush. During that service, Bolton was the "principal architect" in getting the United Nations to repeal its policy of equating Zionism with racism, something he said removed "the greatest stain" on the U.N.'s record.

He graduated from Yale University and Yale Law School.

Rice notified U.N. Secretary-General Kofi Annan (search) and the Senate Foreign Relations Committee, which will hold hearings to confirm Bolton.

Danforth, a former U.S. senator from Missouri, left the United Nations on Jan. 20, saying he wanted to return to his home in St. Louis and spend time with his ailing wife.

FOX News' James Rosen and The Associated Press contributed to this report.