WASHINGTON (AP) – John Kerry, the Democrats’ losing presidential candidate in 2004, said Wednesday that he won’t run for the White House again in 2008.

“Two years ago, I sought the presidency to lead us on a different course,” he said on the Senate floor. “We came close … certainly close enough to be tempted to try again. There are powerful reasons to want to continue that fight now. But I have concluded this isn’t the time for me to mount a presidential campaign.”

The four-term senator and decorated Vietnam War veteran said he would devote his time and energy to ending the conflict in Iraq. Officials also said Mr. Kerry would seek another six-year term in the Senate in 2008.

Mr. Kerry promised to spend the next two years doing whatever he could to ensure that President Bush’s successor enters office with America having “a reasonable prospect of success” in Iraq.

“I don’t want the next president to find that they have inherited a nation still divided and a policy destined to end as Vietnam did – in a bitter and sad legacy,” he said.

Mr. Kerry, 64, who lost the White House when Ohio voted for Mr. Bush by 118,601 votes in November 2004, made the announcement at the end of a lengthy speech on Iraq.

His decision to opt out of the presidential race leaves a field of nine Democrats running or signaling their intention to do so, including Sens. Clinton and Obama, and Mr. Kerry’s 2004 running mate John Edwards.

The Republican field has a similar number with Mr. Bush constitutionally barred from seeking a third term.

Mr. Kerry’s fellow Massachusetts senator, Edward M. Kennedy, spoke on the Senate floor after Mr. Kerry and called him a “true hero.”

“John has decided to continue to devote his passion, his interest, his energies toward bringing our troops home from Iraq safely,” Mr. Kennedy said. “And how fortunate they are to know that he will devote his energies to that cause over the next months, hopefully not years.”

Mr. Kerry’s 2004 campaign drew widespread criticism from fellow Democrats after his defeat. His critics said he had failed to make a forceful enough response to Republican criticism as well as charges by conservative groups that he did not deserve the medals he won for combat in the Vietnam War.

The senator stirred unhappy memories for Democrats last fall, when he botched a joke and led Republicans to accuse him of attacking American troops in Iraq.

He apologized, then hastily scrapped several days of campaigning for fellow Democrats as party leaders urged him to avoid becoming an unwanted issue in a campaign they were on the way to winning.

Polls showed Kerry trailing his Democratic rivals. Last October, an Associated Press-AOL News poll had Mr. Kerry at just 1 percent and recent surveys indicated he had gained little among Democrats.

In a CNN/ORC poll released Wednesday, 51 percent of Democrats said they would not like to see Mr. Kerry run in 2008. When asked who they would support, only 5 percent said Mr. Kerry, placing him fifth and far behind leader Mrs. Clinton at 33 percent.

The Massachusetts lawmaker decided to clarify his political plans on a day in which he participated in a debate over the war in Iraq by invoking memories of Vietnam. At the committee hearing, he said a memorable question he first posed in 1971 had relevance today: “How do you ask a man to be the last person to die for a mistake?”

Despite his difficulties on a national level, Mr. Kerry customarily rolls up large victory margins at home in Massachusetts. He won his first term in 1984.

While Mr. Kerry was saying privately as recently as December that he would likely wage a second campaign, the tone among his aides changed in recent weeks as Mrs. Clinton and Mr. Obama announced their White House bids.

Instead, aides began talking about Mr. Kerry’s concern about the personal toll a campaign would take. Mr. Kerry had millions left from his 2004 run – a sore point with some Democrats. Despite the advantage, he would have faced intense competition with Mr. Obama, Mrs. Clinton and Mr. Edwards for campaign dollars.