By MELODY PETERSEN

he Food and Drug Administration said yesterday that Celebrex, a top-selling arthritis drug, must continue to carry a warning on its label that it can cause serious ulcer complications just as many other pain relievers can.

But in a potential boost to Celebrex, which is in a heated marketing battle with Vioxx, the F.D.A. said the risk of heart attacks among patients taking Celebrex was no higher than for those taking two generic pain medications. Earlier this year, the F.D.A. required that a precaution be added to Vioxx's label about the potential risk of heart attacks.

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The two drugs are crucial products for their makers. Pharmacia and Pfizer sell Celebrex, which had $3.1 billion in sales last year. Merck sells Vioxx, which earned $2.6 billion.

The agency's decision attracted attention yesterday because the government-approved label that comes packaged with each drug directly affects what drug companies can say as they market their products. The label is also considered by doctors to contain the best information on the safety and effectiveness of each drug.

Neither Celebrex nor Vioxx has been shown to reduce pain better than the lower-cost pain relievers like ibuprofen. And the makers of the drugs are trying to persuade doctors and health insurers that the high price of their products is justified by their potential to cause fewer ulcers, which can be a serious side effect of anti-inflammatory pain relievers.

Some Wall Street analysts said yesterday that the label changes might help Pharmacia and Pfizer show doctors that Celebrex is the better choice.

"This is a step ahead of what Vioxx has," said Neil B. Sweig, a pharmaceutical industry analyst with Fulcrum Global Partners, a New York brokerage firm for institutional investors.

But doctors at Kaiser Permanente, a large health insurer, said the F.D.A. decision appeared to give Vioxx an advantage over Celebrex in one specific area — the ability to reduce the risk of serious ulcers. They said it confirmed their belief that Celebrex offered no advantage over older pain relievers available at a fraction of the cost.

"There appears to be no reason to prescribe Celebrex as a first-choice therapy," said Dr. Sharon Levine, associate executive director of the Permanente Medical Group. "Why would you write a prescription for a drug that is many times the cost of Motrin if it is not more effective or safer?"

Dr. Levine said that Kaiser was discouraging its physicians from writing prescriptions for either drug. But if a patient is at high risk of having a serious ulcer complication, Kaiser advises doctors that there may be a benefit from using Vioxx — if the patient is not also at risk of a heart attack.

Those high-risk patients represent about 4 percent of patients taking pain relievers, Dr. Levine said.

When Celebrex and Vioxx were approved, the F.D.A. required both drugs to have the same warnings about ulcers on their label as the older pain relievers. Both Pharmacia and Merck performed large studies to try to persuade the F.D.A. to remove or weaken those warnings.

The F.D.A. changed the warning on Vioxx's label to state that while the risk of serious ulcers was not completely eliminated, it appeared to be significantly lower for patients taking Vioxx than for those taking naproxen, an older pain reliever.

As for Celebrex, the F.D.A. said yesterday that Pharmacia's study did not show that Celebrex was safer on the stomach than either ibuprofen or diclofenac. But the agency said that the results could have been skewed because some study patients taking Celebrex were also taking aspirin, which can cause ulcers.

Dr. Steve Geis, Pharmacia's vice president for clinical research, said the company was pleased that the agency had agreed that specific results from its study could be added to the label, including the very low incidence of ulcers among patients who took Celebrex but not aspirin.

He said that study also proved that Celebrex was safe on the heart. Even when patients in the study were given twice the highest recommended dose of Celebrex, he said, the study showed there was no higher risk of heart attack compared with patients taking diclofenac or ibuprofen.