Making a Donation From the Heart : Medicine: The American Red Cross tries to boost dangerously low blood supplies during its annual drive in the region’s churches.

It took some convincing, but Tim Madden listened to his conscience and gave a pint of his blood Sunday at the third annual Save-a-Life blood drive held at Our Lady of Lourdes Catholic Church.

“The woman who runs this talked me into doing this,” said Madden, lying on a cot and gently squeezing his fist as blood flowed from his body to the intravenous bag. “She said it was my patriotic duty.”

Madden, who said he doesn’t regularly donate but heard there was a need for blood, was one of 700 donors expected to participate in the American Red Cross drive, held at 15 churches throughout Los Angeles and Orange counties in an attempt to bolster the agency’s dangerously low blood supply, spokeswoman Katrina Richardson said.

Although blood supplies are commonly low from mid-December to mid-January, Richardson said the situation is more critical now because blood supplies were below normal for all of 1994.

Last week, the agency issued an emergency appeal urging donations from people with blood types O and B--reserves of which are at one-third the required levels. Nearly half of the country’s population has blood type O, including Sister Rosemarie Karl.

“I am glad to offer it to people who need it, and it doesn’t hurt me to give it,” said the 24-year-old nun, as she nibbled on chocolate chip cookies and sipped juice after donating. “And I was coming to church anyway.”

Mike Hamilton, 52, of Northridge, is a regular donor who heeded the call for more blood and made his way to the parish hall to contribute after Mass. “I normally give blood every year because I have the kind babies need,” said Hamilton, also type O.

In the San Fernando Valley alone, donations dipped from 1,004 units--or pints--in December, 1993, to 871 units last month, Richardson said. Last year’s blood drive attracted only 579 donors, she said.

But the steady flow of donors indicated that things may be on the upswing, at least at Our Lady of Lourdes. “We had 10 people waiting in line before we opened at 8:45 a.m.,” Red Cross head nurse Marti Winkler said.

Locally, other drives were held at St. Clare’s Catholic Church in Canyon Country, St. Jude’s Catholic Church in Westlake Village and Grace Community Church in Sun Valley.