Senator Hillary Rodham Clinton just signed a pledge that commits the next president to investing $50 billion by 2013 to combat AIDS around the world. She is also planning to deliver a formal policy on AIDS.

Gay and lesbian activists have been asking the presidential candidates to sign the pledge, which is being circulated by a global AIDS alliance.

Among the Democratic candidates, only Bill Richardson had signed the pledge. John Edwards and Barack Obama have issued AIDS plans and have agreed to many of the pledge’s goals but have not signed it.

ACT UP, a coalition of gay and lesbian activists, had been planning a demonstration against Mrs. Clinton on Tuesday in Philadelphia, where the Democratic presidential candidates are meeting for a debate. Some activists had been complaining that she had not signed the pledge.

But when The Caucus contacted the Clinton campaign, a spokesman said that Mrs. Clinton would sign the pledge shortly; moments later she did.

“Senator Clinton has been working on a formal AIDS policy that she will be unveiling in the near future,” a statement from the campaign said. “She already supports investing $50 billion over the next five years to fight global AIDS and advocates a comprehensive approach to fighting AIDS both here and abroad.”

Initially, ACT UP, which has been demonstrating on behalf of people with AIDS for nearly 20 years, announced that it would march against Mrs. Clinton at the debate Tuesday. Kaytee Riek, a member of ACT UP and a member of Health GAP, an organization that is also sponsoring the demonstration, said that the protest was aimed at Mrs. Clinton because “she’s the front-runner,” even though she has a “spectacular” record on AIDS. She also said that Mr. Edwards and Mr. Obama had already put out plans that would achieve many of the goals stated in the pledge.

But informed subsequently that Mrs. Clinton had signed the pledge, Ms. Riek said, “That’s excellent!” She also said that this would probably change the focus of the demonstration on Tuesday to urge all candidates to make discussion of AIDS a campaign priority.

Mr. Edwards was the first to issue a comprehensive AIDS plan that includes $50 billion, which Ms. Riek said was “excellent.”

Senator Obama has said that as president, he would double foreign assistance from $25 billion per year to $50 billion per year for numerous projects, including the treatment of AIDS and other diseases like tuberculosis and malaria. In outlining his “millennium development goals,” Mr. Obama’s campaign said he would “dedicate as much funding to HIV/AIDS as possible — without cutting into other critical foreign assistance programs — to ensure a comprehensive fight against this global pandemic.”

Mrs. Clinton has addressed numerous aspects of the AIDS issue, including the racial disparities that ACT UP has said is one of its chief concerns.

“If HIV-AIDS were the leading cause of death of white women between the ages of 25 and 34, there would be an outraged outcry in this country,” Mrs. Clinton said at a forum in June at Howard University. She also said she was committed to getting Medicaid to cover AIDS treatment