Blood supplies across the region have dipped to critically low levels, donor services said last week, the result of an annual summer slowdown in giving that is more severe this year.

Officials for both the Greater Chesapeake and Potomac Region of the American Red Cross and Inova Blood Donor Services said blood reserves have dropped well below the one-day supply mark.

Both groups, which are the major blood suppliers in the Washington region, are putting out the warning and appealing for donations.

Officials of the groups said summer is always hard on the blood supply because many potential donors go on vacation. But this year has been particularly difficult, said Tracy M. Laubach, director of marketing and communications for the regional Red Cross. She said that a yearly drop-off that occurs just before the Fourth of July holiday hit earlier this year and that unlike in past years, giving has remained slow.

"It's put our inventory at a level that is just not safe," she said. "People are just busy. They're on vacation, they've got family in town and schools are out of session. A huge portion of our supply comes from high schools and colleges."

The regional American Red Cross group, one of 35 across the country, supplies blood to 65 hospitals across Maryland, Washington, Northern Virginia and parts of Pennsylvania, including 10 trauma centers. Inova Blood Donor Services gathers blood for an additional 15 hospitals, two with trauma centers, including Northern Virginia's Inova Health System hospitals and clinics.

Laubach said the Red Cross depends on 1,100 to 1,300 donors every day but has been getting about 900. Inova needs 200 donors a day but has been getting only 60, said Linda Wilson, the service's donor recruitment manager. Inova Blood Donor Services has been offering each donor a $10 gas card as a thank-you giveaway that will continue through the end of the month.

"For each day you fall a couple hundred short, and then a couple hundred short the next day, it really adds up over time," Laubach said.

The low supply is endangering both groups' ability to meet their hospitals' routine blood requirements for trauma and surgical patients as well as premature babies and others who might need transfusions, officials said.

The shortage also means, they said, that the region is ill-prepared for a terrorist attack such as the subway and bus bombings in London on July 7 that killed more than 50 people. They said it takes about 48 hours to screen, package and label donated blood, meaning that hospitals cannot rely on instant donations to fulfill immediate blood needs during an emergency.

"The blood needs to be there before the need," Inova's Wilson said.

Compounding the problem is that blood banks nationwide are experiencing the same shortages, she said, so there is no one to whom the Washington region can appeal for more blood -- other than local residents.

Though it is safe to give blood as often as once every eight weeks, the average donor gives 1.6 times a year. Less than 5 percent of eligible donors give at all.

Both organizations strongly prefer that donors make an appointment before giving blood but can accommodate walk-ins. More information about giving blood in Southern Maryland, including contact information for donor centers, can be found by calling the American Red Cross at 800-GIVELIFE or by contacting the Southern Maryland chapter directly at 301-934-2066.

Connie Ream prepares Crystal Catterton to give blood in Lusby in 2001. Area reserves are below a one-day supply, donor services said.

Inova Blood Donor Services is giving $10 gas cards to donors until the end of the month.