WASHINGTON — President Bush signed legislation today that triples American funding to fight AIDS, malaria, and tuberculosis around the world.

The five-year, $48 billion plan renews a program credited with saving millions of lives in Africa alone and is widely seen as one of the major achievements of the Bush presidency.

Mr. Bush said the program, launched by him in 2003, “is the largest commitment by any nation to combat a single disease in human history.”

The president signed the bill in the ornate East Room of the White House, surrounded by lawmakers and people affected by AIDS whom he met on his February trip to Africa.

The legislation is a rare case of relatively easy cooperation between the Democratic-controlled Congress and the White House. It passed the House last week by a 303-115 vote and the Senate earlier in the month by a vote of 80-16.

It renews Mr. Bush’s original five-year, $15 billion program called the President’s Emergency Plan for AIDS Relief, which was set to expire in September.

Some GOP conservatives questioned the new plan’s sharp spending increase. But most on both sides of the aisle, and in groups that advocate both health initiatives and Africa, praised the American aid for boosting America’s reputation abroad.

Mr. Bush diverted from broader remarks to issue a personal appeal to those stricken with AIDS.

“Don’t let shame keep you from getting tested or treated,” he said. “Your life is treasured by the people who love you. … It matters to the people of the United States.”

The AIDS initiative has so far supported care for nearly 7 million people and helped deliver lifesaving anti-retroviral drugs to about 1.7 million HIV-positive people. With the AIDS pandemic now affecting 33 million people worldwide, both Democrats and Republicans have called it one of the most significant accomplishments of the Bush presidency.

The program’s five-year renewal comes with some significant changes that took months to negotiate: a third of prevention funds will no longer be reserved for abstinence education; a “conscience clause” gives religious groups the right to refuse participation; more focus is placed on women and girls, and HIV-positive people will find it easier to get visas into America.

Mr. Bush said the goal for the new funding is to prevent 12 million new HIV infections, treat more than 2 million with anti-retroviral drugs, support care for 12 million, and train at least 140,000 new health care workers.