The rooms where abortions are performed were dark and cold at 2 a.m. yesterday, but the rest of the clinic was lit up and occupied by tired volunteers, keeping a vigil around the clock. They sipped coffee, played a computer trivia game and took turns sleeping and standing outside in the frigid night, on the lookout for potential bombers.

The scene at the Women's Medical Center of Washington was replayed across the country this weekend at more than 30 abortion clinics -- including one in Falls Church and one in Fairfax County. Members of the National Organization for Women and other volunteers moved in Friday and, in some cases, will stay until Wednesday to prevent violence against the clinics, as abortion foes march on Washington today, the 12th anniversary of the Supreme Court decision that declared abortion legal.

"I was not going to see us sit back and just wait to be bombed," said Gail Robinson, an administrative assistant for a legal association and coordinator of the D.C. chapter of NOW. "No one else was doing anything" in response to a recent rash of attacks on abortion clincs around the nation, she said. The vigils did not receive the support of some other prochoice groups, including the Planned Parenthood Federation of America and the National Abortion Federation.

Robinson, who spent her weekend at the clinic in downtown Washington, shared the Sunday night watch with more than a dozen men and women, each of them professing their determination to fight the antiabortion movement.

Among them was Laura Winick, a 24-year-old sign language interpreter who said she joined the vigil because she has had two abortions and wants to fight to protect others' right to abortions.

Another in the group told of being "harassed" by protesters when she went for an abortion several years ago.

"I just wanted to fight back," said the woman, who asked not to be named.

While the Women's Medical Center -- which performs 35 to 40 abortions a week -- received bomb threats Friday and Sunday, there was no reported violence at clinics this weekend, NOW officials said.

The atmosphere at the clinic was somewhere between a sit-in and a pajama party. Those on vigil slept intermittently, spread out in sleeping bags on the clinic floor, waking to take watch duty outside the white marble office building and at the elevator entrance on the seventh floor, where the clinic is located.

Other volunteers padded around the clinic in stocking feet and fur-lined slippers, living on take-out Chinese food and soft drinks stored alongside petri dishes in the lab refrigerator.

"We've had a good time, but it hasn't been a party atmosphere," said Robinson. "After the bomb threat Friday I got scared. A bombing seemed a lot more real at that point."

That night, the volunteers nervously kept note of suspicious vehicles and passed around a composite sketch from police of a suspected bomber, one of three men arrested Saturday in connection with eight bombings of clinics and prochoice facilities. "Every man who walked by looked like him," said Lisa Lederer, NOW press officer.

Lederer and the others at the clinic said they were relieved Saturday by the arrests, but the group maintained its preordained protocol of strict security.

"Only a hopeless Pollyanna could have said that because of the arrests of those three people the problem was over," said NOW national President Judy Goldsmith, who spent two nights at the clinic.

Despite hundreds of offers of help, only persons known to the vigil organizers were allowed in the clinic. Rigid sign-in sheets were maintained by a building security guard and even expected visitors were required to show identification.

But by Sunday night, the volunteers had relaxed, at least those huddled over cribbage boards and watching television inside the clinic. "When you're standing outside at 3 in the morning looking for crazies . . . . That's when you feel serious," Lederer said.

Goldsmith reported similar scenes at other NOW clinics. At the Commonwealth Women's Clinic in Falls Church, those on vigil were sent meals from neighborhood church women and doughnuts and coffee from a nearby restaurant, she said.

While the antiabortion forces gather today, the clinic watchers are dispersed to their normal jobs and routines. They parted Monday morning with the camaraderie of a weekend retreat.

"It's been a tremendous experience," said Goldsmith in bidding goodbye. "Maybe we should all room together next semester."