Officials of the American Red Cross, suppliers of 90 percent of the blood used for transfusions in D.C. area hospitals, yesterday reported dangerously low levels of type-O positive and type-B positive blood and urgently are seeking donors.

A traditional summer dip in supply has been exacerbated this year by unusually heavy demands from hospitals for blood, Red Cross official said.

"People on vacations put a dent in our donor base because they usually forget to give before they go out of town," said Red Cross spokesman James MacLeod. However, the need for blood does not decrease, MacLeod said, and this year the situation is worse than usual.

Hospital demand, normally 3,500 to 3,800 units of blood daily, exceeded 4,000 units daily during the first three weeks in May, according to Dr. Paul McCurdy, director of Washington-area blood services for the Red Cross. A unit of blood is approximately one pint.

"Now we have less than a one day supply of O-positive on hand," McCurdy said yesterday. "We have been in this emergency situation for more than a week."

Type-O positive, which can be used in a much wider range of situations than other types, is always in short supply even during peak donation periods, McCurdy said.

None of the hospitals supplied by the Red Cross here has been forced to postpone scheduled surgery because of blood shortages. McCurdy said he worries that a patient requiring more than 150 units of blood might bleed to death, given the existing low supply levels.

"Monday, a bleeder at the University of Virginia Hospital in Charlottesville used 150 units of O-positive blood," said McCurdy. "That's a two-day collection. If we were to get a 150-unit bleeder today we would have great difficulty coping."

Cynthia Byers, spokeswoman for the Georgetown University Medical Center, said the hospital's supplies of O-positive blood are below normal. Byers added that "we're okay unless a crisis develops."

Four million people live in the Red Cross' Washington Regional Blood Services area, MacLeod said. "Only 3 to 4 percent of these people are blood donors," he said.

He said anyone who weighs at least 110 pounds, is between 17 and 66 years old, is in good health and has never had hepatitis can donate blood.

People wanting to donate blood should contact their local Red Cross chapter for the donor location nearest them, or call 857-3400 for additional donor information. The Red Cross permanent Donor Center is located at 20th and E streets NW. Those who wish to donate may call 857-3553 for an appointment and hours of operation.