WASHINGTON — Experts at an early August international AIDS conference in Mexico City were full of praise for the United States for having reversed a 15-year-old law banning HIV-positive people from entering the country.

But nearly two months after President Bush signed that act into law, his administration has yet to take the steps needed to put the new law into practice, and lawmakers and advocacy groups are wondering what is going on.

"We write to encourage you to act quickly to remove HIV from the list of communicable diseases of public health significance and end the HIV travel and immigration ban," Sens. John Kerry, D-Mass., and Gordon Smith, R-Ore., main backers of the measure in the Senate, wrote to Health and Human Services Secretary Mike Leavitt last month. Leavitt is a former governor of Utah.

Fifty-eight House Democrats last week went right to the top, writing a letter to Bush that urged him to take "swift action on this issue." The signees included California Reps. Barbara Lee, chief sponsor in the House, House Oversight Committee Chairman Henry Waxman, and House Foreign Affairs Committee Chairman Howard Berman, all California Democrats.

Last July 30, Bush signed into law a five-year, $48 billion bill to fight AIDS, malaria and tuberculosis around the world and to end the ban on HIV travelers.

But before the statutory ban can effectively be ended, HHS must write a new rule, submit it for public comment and finalize it.

"Congress has sent a clear signal that we can't fight discrimination and stigma abroad until we end them at home," said Victoria Neilson, legal director of Immigration Equality. "Congress has done its part — it's time for HHS to act."

"We're working hard to revise the regulation, and it's our goal to have it completed during this administration," said HHS spokeswoman Holly Babin. She said it was "a time-consuming process, and we are giving it the attention it deserves in an effort to anticipate all issues and get it right."

HHS added HIV to the list of communicable diseases that disqualified a person from entry in 1987, a time of widespread fear and ignorance about the disease. The department in 1991 tried to reverse that decision but was opposed by Congress, which in 1993 went the other way and made HIV infection the only medical condition explicitly listed under immigration law as grounds for inadmissibility.

While there is a cumbersome waiver process, the law has effectively kept out thousands of students, tourists and refugees and complicated the adoption of children with the AIDS virus. No major international AIDS conference has been held in the United States since 1993 because activists or researchers who have the virus can't gain entry. There's also concern that foreign nationals in the country with the virus might not seek treatment because of fears of being deported.

Only about a dozen countries around the world, including Libya, Russia, Saudi Arabia and Sudan, ban travel and immigration for people with HIV.

U.N. Secretary General Ban Ki-moon, at the August conference in Mexico City, said the restrictions, also imposed by his own country, South Korea, "should fill us with shame." Others at the conference praised the United States for ending its ban and said that could set a precedent for other countries that exclude people with HIV.

Advocates said that having won international plaudits for the new law, it's time to follow through.

"We'll continue to pressure Secretary Leavitt to finish the job and eliminate regulations that keep that unfair policy in place," said Allison Herwitt, legislative director at the Human Rights Campaign, the nation's largest gay rights organization.