ASHINGTON, Feb. 2 — Citing Sept. 11, representatives of New York's health care industry are urging the federal government to postpone and, if necessary, abandon a new policy that would place a severe strain on the region's dwindling blood supply.

The policy, which the Food and Drug Administration plans to put into effect this spring, directs blood banks to turn away any donors who may have been exposed to mad cow disease while in Europe.

The agency has acknowledged that it has little scientific basis to believe that humans could contract the disease through a blood transfusion. But it has moved to put the policy into effect anyway, arguing that it is better to err on the side of caution.

But now, in the wake of the terrorist attacks, New York health care officials warn that the donor ban would worsen a deepening blood shortage in the metropolitan region and make it impossible for hospitals to cope in the event of future disasters.

The concern among health care officials has been heightened because blood donations in Manhattan have dropped by 3,000 pints a month — or 25 percent — since the attack on the World Trade Center. In the New York region, donations have dropped by 6,000 pints, or 15 percent.

The lobbying effort is being led by the office of Charles E. Schumer, New York's senior senator, who had previously backed the F.D.A.'s donor restrictions, although reluctantly.

Mr. Schumer has sent a letter to the secretary of health and human services, Tommy G. Thompson, whose agency has authority over the F.D.A., asking him to overrule the agency's decision.

In an interview, Mr. Schumer explained that he had been willing to go along with the F.D.A.'s donor ban before Sept. 11. But now, he said, the policy is ill advised, particularly since there is no documented case of mad cow disease being spread through blood transfusions.

"The danger of not having an adequate blood supply has been highlighted by the events of Sept. 11," he said.

Blood bank officials say the attack wiped out a large part of their donor base in Lower Manhattan, where businesses and other organizations provided a steady supply of blood through regular donor drives.

"Think about it," said Dr. Robert L. Jones, the president of the New York Blood Center, which supplies blood to 200 hospitals in the region. "The World Trade Center has disappeared. We used to run blood drives in many of the businesses and organizations that were in there. Now, they're gone.

"We're not sure how we're going to recover from that loss," he said.

The president of the Greater New York Hospital Association, Kenneth E. Raske, echoed those concerns. "We are facing a major problem that could get worse quickly," he said. "This is like a drought warning."

The F.D.A. policy calls for excluding blood donations from anyone who has spent five years or more in Europe since 1980, or three months or more in Britain from 1980 to 1996. In effect, it would ban any blood imported from Europe.

The restrictions would be applied nationally, but would hurt the New York metropolitan region the most, since it is the only place in the country that imports blood from Europe, according to health care experts.

In all, the New York region imports one in every four pints — 145,000 pints a year — from Europe.

Hospital administrators and blood bank officials in New York strongly objected to the donor ban when it was first proposed last year. But they dropped those objections after two of the nation's major blood banks came forward and offered to make up the shortages caused by the new policy.

Now, hospital administrators and blood bank officials in the New York region are questioning whether they can count on those promises of help, since other parts of the country are reporting blood shortages.

"There's nothing to back up that commitment," said Dr. Jones. "There's no supply that's in place to replace the Euroblood."

In his letter, Mr. Schumer urged Mr. Thompson to delay the donor ban until the F.D.A. identifies a new source of blood to help New York City hospitals meet their current demands — as well as any demands that might arise in the event of a future terrorist attack.

"You may recall that I did not dispute the F.D.A.'s decision to show extreme caution and ban the importation of blood from Europe," Mr. Schumer wrote. "As you well know, we now live in a very different world.

"Even if we once had the luxury of showing extreme caution and banning the importation of blood from Europe (albeit without actual scientific evidence of a problem) before Sept. 11, without an alternate solution, that luxury no longer exists," Mr. Schumer continued.

"The F.D.A. cannot leave New York vulnerable, even if that means changing its position on banning blood from Europe."

Bill Pierce, a spokesman for Mr. Thompson, said he would consider Mr. Schumer's request. But he strongly suggested that Mr. Thompson would not overrule the F.D.A. "He does not want to compromise the safety of the blood supply or shake the public's confidence in the blood supply," Mr. Thompson said, echoing the rationale the F.D.A. offered when it proposed the donor ban.