WASHINGTON – The Food and Drug Administration wants the power to write warning labels for drugs, telling Congress yesterday it would help end the haggling with pharmaceutical companies that delayed warnings to Vioxx users about potential heart problems.

The FDA now is not permitted to write the warning labels and must negotiate wording with manufacturers. Usually that poses no problem, said Sandra Kweder, deputy director of the Office of New Drugs.

But when Vioxx’s side effects became known, Merck & Company and the FDA engaged in a tug-of-war over the label’s language, Ms. Kweder said.

“The lapse from my perspective was the delay that it took to get that information into the labeling,” Ms. Kweder told the Senate Committee on Health, Education, Labor, and Pensions.

“A strong ability to require changes in labeling would be helpful,” she said.

She also praised the Bush administration’s newly-announced policy to publicize warnings before such sticking points are worked out. Merck pulled Vioxx from the market September 30 after heart problems were reported in some users. Similar questions were later raised about other so-called Cox-2 inhibitors – Bextra and Celebrex – leading the FDA to direct an advisory panel to look into the matter.

The advisory panel on February 18 decided that the arthritis drugs’ benefits outweighed the risks of heart problems and strokes but suggested the products carry strong warnings.

On Monday, Massachusetts-based Mogen Idec Inc. and Elan Corp. announced they were pulling a drug to treat multiple sclerosis after it triggered a serious disease in two patients – killing one of them – when taken with other drugs.

Congress is considering legislation to tighten rules on how the government keeps track of the safety of drugs after the FDA approves them.

The proposals include a bill unveiled Monday that would require drug and medical-device manufacturers to report findings of clinical trials in a publicly available database, including potential side effects, funding, and information on test subjects.

The hearing yesterday may produce legislation on tightening the FDA’s approval process and rebuilding public confidence in the agency, said Chairman Michael Enzi, a Republican of Wyoming. But he cautioned against regulating drug approval so tightly that risks are not properly weighed against benefits.

“Every time we take a drug, we take a risk, so we should not overreact to recent events,” Mr. Enzi said.

Senator Kennedy, a Democrat of Massachusetts, agreed, but said Congress can enact safeguards that work.

The FDA, he said, “needs clear authority to require relabeling of a drug if necessary after approval, once a risk is found.”

The administration announced last month it would set up an independent Drug Safety Oversight Board to monitor FDA-approved medicines once they’re on the market and update physicians and patients with emerging information on risks and benefits.