Sen. John Kerry of Massachusetts, the 2004 Democratic presidential nominee, intends to endorse Sen. Barack Obama for the White House in a timely slap at Sen. Hillary Rodham Clinton as well as his own vice presidential running mate.

Kerry planned to deliver his endorsement in South Carolina at a time, two weeks before that state’s primary, when Clinton is riding a wave of enthusiasm following her victory over Obama in the New Hampshire primary.

Former Sen. John Edwards of North Carolina, the third contender in the Democratic presidential race, was Kerry’s vice presidential running mate in 2004. Despite their political alliance, the two men were not close personally and differed behind the scenes on campaign strategy in a race that President Bush won.

Edwards responded to word of the endorsement with a diplomatic statement: ”Our country and our party are stronger because of John’s service, and I respect his decision. When we were running against each other and on the same ticket, John and I agreed on many issues.”

Kerry was Obama’s political benefactor once before, selecting the relatively unknown Illinois senatorial candidate to deliver the keynote address at the 2004 Democratic National Convention in Boston. It was Obama’s first turn in the national spotlight and helped launch him on a remarkable ascent that has made him one of two leading contenders for the party’s presidential nomination only four years later.

Kerry planned to announce his endorsement at a rally with Obama at the College of Charleston.

The Massachusetts senator lost the South Carolina Democratic primary in 2004 to Edwards.

Kerry and Edwards had their differences during the 2004 campaign over strategy and spending, and Edwards has said he would have been more aggressive in challenging the unsubstantiated allegations of the Swift Boat Veterans for Truth questioning Kerry’s military record.

Kerry’s endorsement also was a jab at Clinton, the New York Democrat who won the New Hampshire primary after a loss to Obama in the Iowa caucuses.

Kerry had withheld his endorsement, hoping to have an impact on the race and avoid the fate of fellow Democrat Al Gore, the 2000 nominee who endorsed Howard Dean in 2004 shortly before the former Vermont governor’s campaign imploded. Gore has made no endorsement so far this year.

While Kerry has been close to Clinton’s husband, the former president, he was incensed in 2006 when she chided him after Kerry suggested that people who don’t go to school ”get stuck in Iraq.” Aides said Kerry meant to jab at Bush and say ”get us stuck in Iraq,” and that he didn’t appreciate Clinton piling onto the criticism he was already getting for the remark.

Kerry himself had considered running for president in 2008, but that plan fizzled with the botched remark. For many Democrats, his words revived bitter memories of his missteps in 2004, when he lost to Bush.

As for Obama, Kerry gave the young Illinois state senator his first turn in the national spotlight when he chose him to deliver the keynote speech at the 2004 Democratic National Convention. Later that year, Obama won election as a U.S. senator.

Since announcing a year ago he would not make the run, Kerry has prodded Democrats to take a stronger anti-war stance, pushing for troop withdrawal deadlines. In another area, he has backed environmental causes, writing a book with his wife on the issue.

Kerry should be able to provide some organizational muscle to Obama.

Since losing the 2004 race, Kerry has kept a national network of supporters intact. He has an e-mail network of 3 million supporters, according to aides. He also has traveled extensively raising millions of dollars for Democratic candidates nationwide.