Florida Sen. Bob Graham (search) said Monday he will not seek re-election to a fourth term in the U.S. Senate.

"I will not be a candidate for election to a fourth term," Graham announced as he stood in front of a group of students from Lincoln High School in Tallahassee. The senator, who ended his bid for the Democratic nomination for president last month, was at the school for a "work day," in which he was working with construction workers on a new school roof and athletic track.

"I do not say this because I feel that all of my goals have been accomplished," Graham said, before he paraphrased a remark once said by the late British leader Winston Churchill (search): "This is not the end. This is not the beginning of the end. Perhaps, it is the end of the beginning."

Calling his decision "very difficult" for both himself and his family, Graham said he wants to continue his public work, including creating an institute to train future Florida leaders and helping to improve national security. He also wants to spend more time with his wife, Adele, children and grandchildren.

A source close to Graham told The Associated Press that the lawmaker has pledged to help the Democratic Party keep the Senate seat.

"Bob Graham's departure is a tremendous loss for the Senate, for Floridians, and for the nation," Senate Minority Leader Tom Daschle, D-S.D., said in a statement Monday. "Few public servants can match Bob Graham's breadth of experience or depth of knowledge."

Graham's decision had been a tightly kept secret. His staff wasn't informed until 7 a.m. Monday on what the decision would be and even the Democratic Party had two versions of a press release waiting — one for if he ran, one for if he quit.

Graham's chief of staff made calls to the other campaigns late Monday morning.

Graham, a former two-term governor, is considered one of the most popular politicians in Florida, where he has served in the Senate since 1987.

The Sunshine State is expected to be critical to both presidential politics and congressional politics in 2004. So Graham's announcement further complicates Democrats' hopes to regain control of the Senate, where Republicans hold a 51-48 majority, with one Democratic-leaning independent.

"The only consolation in Bob's announcement is that there are a number of strong candidates who are ready to follow in Bob's footsteps and who have already laid the groundwork for successful Senate campaigns," Daschle said.

"I'm confident that Florida will be eager to fill Bob's seat with someone who can represent Florida's values and priorities as faithfully and forcefully as Bob has these past 17 years."

Four Democrats — U.S. Reps. Peter Deutsch (search) and Alcee Hastings (search), Miami-Dade Mayor Alex Penelas (search) and former state Education Commissioner Betty Castor (search) — had declared for Graham's Senate seat but said they wouldn't challenge Graham if he sought re-election.

Republicans seeking Graham's seat include state House Speaker Johnnie Byrd (search), legal activist Larry Klayman (search), former U.S. Rep. Bill McCollum (search) and state Sen. Dan Webster (search) of the Orlando area.

While the state GOP said his presidential campaign might make him vulnerable, analysts considered Graham to be a strong candidate for re-election.

Graham is the fourth Southern Democrat to announce plans to retire at the end of his term, giving Republicans opportunities for strong gains in a region of the country where President Bush figures to run strongly in 2004.

Others retiring include: Sens. Zell Miller of Georgia, John Edwards of North Carolina and Ernest "Fritz" Hollings of South Carolina.

"Democrats, all Floridians, will be sad to see him go, but we know he stands ready to continue to serve America and Florida," said Florida Democratic Party Chairman Scott Maddox.

Graham, who has built a reputation for his low-key, methodical approach to legislation, served last year as chairman of the Senate Intelligence Committee, where he was at the forefront of the debate over the nation's preparedness against terrorism.

Graham is currently the ranking minority member of the Senate Veterans' Affairs Committee, and also sits on the Finance, Environment and Public Works and the Energy and Natural Resources committees.

He is also chairman and founder of the Senate New Democrat Coalition and is involved with the Senate Caucus on International Narcotics Control, Senate Democratic Pension Task Force, National Security Caucus and the Senate Rural Health Care Caucus.

Graham, who turns 67 on Sunday, delayed his entry into the presidential contest to recover from major heart surgery in January. He based much of his campaign on his vote against the military conflict in Iraq. Yet anti-war activists preferred former Vermont Gov. Howard Dean's fist-pounding indignation to Graham's calm, measured arguments against President Bush's foreign policy. Graham's presidential fundraising was also weak.

He was the only White House candidate from the Senate to have voted against the Iraq war resolution last October.

Graham accused Bush of endangering Americans by abandoning the fight against terror to wage war in Iraq, which he said did not pose an immediate threat to the United States.

He cited a "Nixonian stench" in the White House, arguing the Bush administration formed a pattern of keeping information from the American people while calling Bush's tax cuts "immoral."

He went so far as to suggest impeachment.

"If the standard of impeachment that the Republicans set for Bill Clinton — a personal, consensual relationship was the basis for impeachment, would not a president who knowingly deceived the American people about something as important as whether to go to war meet the standard of impeachment?" he said in July.

He handily defeated current Attorney General Charlie Crist in 1998 with 62 percent of the vote and has not faced a serious challenge since defeating Sen. Paula Hawkins in 1986.

Fox News' Julie Asher, Carl Cameron and The Associated Press contributed to this report.