WASHINGTON — President Bush, after a lengthy search, yesterday nominated longtime acting commissioner Lester Crawford to head the Food and Drug Administration, despite drug-safety problems on Crawford's watch that have undermined the agency's reputation and credibility.

The appointment of an FDA commissioner had been eagerly awaited by consumer groups and lawmakers, some of whom have criticized the agency for responding too slowly to the discovery that prescription drugs ranging from painkillers to antidepressants and acne medications have been approved even though they were found to have dangerous side effects.

By sticking with Crawford, 66, a pharmacologist and veterinarian who has been running the agency for almost a year, Bush disappointed those who had hoped for a nominee who would bring dramatic reforms.

"I do not think [Crawford] should be confirmed unless he is able to articulate some strong priorities that will restore confidence in the FDA," said one critic, Janell Mayo Duncan, a lawyer for Consumers Union and an assistant FDA chief counsel for enforcement from 1996 to 1998.

But an administration official, who asked not to be identified, said, "I think the FDA has gotten a bum rap, and some people may be trying to transfer that bum rap to Dr. Crawford."

As acting commissioner, Crawford launched an independent scientific evaluation of the FDA's drug-safety program and won White House approval for an increase of roughly 20 percent in the budget of the safety office.

Two recent debacles have heightened concerns about the FDA, which is charged with ensuring that medicines sold in the United States are "safe and effective."

In one case, the FDA moved to warn of risks of suicidal behavior for teenagers taking antidepressants only after regulators in other countries acted.

And late last year, the agency was overwhelmed by the emergence of heart risks with Vioxx, Celebrex and other painkillers of a class known as Cox-2 inhibitors. Doctors and patients were thrown into confusion by a series of studies, each documenting a new problem.

"I want to hear statements that prove he understands why public confidence has been shaken, and a commitment to enacting reforms inside the FDA to keep the agency focused on public health and safety," said Senate Finance Committee Chairman Charles Grassley, R-Iowa, who held hearings last year on Merck's decision to recall Vioxx after a study confirmed that it could lead to heart attacks and strokes.