With next week's Wisconsin primary looming, Clark plans to join Kerry at a campaign stop in Madison, Wis., Friday to make a formal endorsement, said officials, speaking on condition of anonymity.
Clark spokesman Matt Bennett would not confirm the endorsement, and would only say, "General Clark is looking forward to going to Wisconsin to be with Senator Kerry."
Kerry has racked up wins in 12 of 14 Democratic contests and hopes to add Wisconsin to his win column. The backing of Clark, who registered in the low double digits in earlier Wisconsin polls, could increase Kerry's advantage in a state with 72 pledged delegates at stake.
The Southern-bred Clark dropped out of the race for the White House on Wednesday after disappointing third-place finishes in Tennessee and Virginia. The retired four-star general was unable to command significant support as a first-time presidential candidate, winning just one state Oklahoma in 14 contests.
He coupled his withdrawal with words of praise for his remaining rivals Kerry, Sen. John Edwards and former Vermont Gov. Howard Dean.
"They're good men, they're good Democrats and they're good patriots," Clark said. "Our country is well-served" by them, he added.
Clark, a 59-year-old career military man, burst onto the campaign last fall, supplanting his more experienced and better-known rivals at the top of the polls and demonstrating significant fund-raising ability.
The commanding general in NATO's war in Kosovo in 1999, Clark anchored his political appearances with a pledge of "a higher standard of leadership" and spoke to campaign audiences often of service, duty and honor.
Strategically, his first key decision was to bypass the kickoff Iowa caucuses in favor of the New Hampshire primary eight days later. Kerry's surprise caucus triumph trumped Clark's plan, and the former general faded to a distant third.
After Kerry won a surprise victory in the Iowa caucuses, Clark suggested that Kerry's experience as a Navy lieutenant could not match his own as a four-star general. He toned down his remarks, saying he wasn't trying to distinguish between his rank and Kerry's.
Clark wrestled with the decision to end his campaign as election returns rolled in Tuesday night, with advisers urging him to quit and family pushing him to continue. Before deciding to exit, he thanked several hundred cheering backers.
"We may have lost this battle today, but I tell you what, we're not to lose the battle for America's future," he said Tuesday.
Aides said Clark would remain active in the campaign by stumping for Democrats in the South and other swing states and serving as an adviser on national security issues.
In appealing to voters, Clark relied almost entirely on his 34 years in military service. Supporters touted other qualities his Southern roots and his status as a Washington outsider that they contended made Clark the candidate most likely to defeat Bush. Plus, he provided another forceful voice in condemning the war in Iraq, which he frequently called unnecessary, reckless and wrong.
Clark had enormous fund-raising success for a latecomer, raising nearly $15 million in 2003. He started January with at least $10 million left and the prospect of raising millions more.