The headquarters of the National Organization for Women hums with the activity of a political campaign as workers prepare for the "National March for Women's Lives" on Sunday.

It is expected to be one of the largest demonstrations for abortion and birth control rights in the history of the NOW organization, which marks its 20th anniversary this year, with the aim of removing an antiabortion amendment from the proposed Civil Rights Restoration Act.

The pressure on NOW and other women's organizations to accept the amendment as the tradeoff for passage of the civil rights act has fired up the troops, NOW officials say, and volunteers arrive daily.

Loretta Ross, director of NOW's Women of Color Program, noted that of the 49 predominantly black groups endorsing the march -- from a local charity group, "Lord, I Don't Want My Work To Be in Vain," to the Free South Africa Movement -- only eight previously had been involved with NOW.

"More people are realizing that if abortion is outlawed, everybody gets hurt," Ross said. "Black women are finding that this is an issue that they can work on with white women. Others, who threw their birth control pills away to have a baby for the 'revolution,' have changed their minds."

With the recent defeat of antiabortion referendums in California and other states and political victories for blacks and women in Virginia, NOW feels that this will also be a time for celebration.

Its ranks have grown from 28 in 1966 to more than 150,000 today. Despite the persistent opposition led primarily by male religious leaders, poll data now show that the majority of Americans are prochoice.

Converts include many men, such as Wendell Packard, 59, and Harold Shambaugh, 64, who work as volunteers in the mail room at NOW headquarters in downtown Washington.

"The change in my attitude has been about 180 degrees," says Shambaugh, a retiree who lives in Silver Spring. "I developed some very chauvinistic, right-wing views in the military. But with my wife's help, I was able to see the inequities that exist, so when NOW called asking if she would be a volunteer, I said, no, because she works. I volunteered."

"The newer women still look at us with some suspicion," said Packard, a retired civil engineer from Camp Springs.

"They wonder what these two middle-aged men are doing here. All we can do is say, 'We'll do anything you ask.' "

The office walls are decorated with color prints of women in sports: playing tennis, baseball and soccer.

It is bright and lively, but that does not alleviate the fact that offices of prochoice groups have been the sites of violent demonstrations against abortion and birth control.

In 1984, 32 clinics were bombed.

More than nine incidents were reported in the Washington area.

These acts of "terrorism" failed to deter the movement, NOW officials say, and the group members feel they have achieved the moral upper hand.

"We feel strongly that we are winning," one NOW volunteer said.

"Birth control is an economic issue for women and their families. In most loving relationships, men and women have a say. But we do have abusive relationships, and then the person who must bear the brunt of the pain must have the right to make the decision for herself."

"There are forces that just want a larger poverty class," one NOW volunteer said. "They want to create dependence so they can work for less wages."

The volunteers are adamant in their stand and can be expected to send a profound message next weekend.

The fight is not just for women's lives but for better lives, and against poverty and economic exploitation.

Kim Fredrickson, 26, flew in from her home town, Tacoma, Wash., and spent yesterday fashioning collection baskets from plastic bags for the march.

"Every time there is a threat to our rights we have to stand up for what we believe in," she said.

On each bag she placed a sticker: a picture of a bloody clothes hanger that read, "Never Again."