MORE THAN 3,000 women came to Washington Wednesday from across the country to tell members of Congress that women didn't drop off the face of the earth on Nov. 5. Organizers had expected 1,500 people to show up. That double the number came made their day. They're hoping it also made a point.

Women's Rights Day was organized by some 80 groups ranging from the American Association of University Women, B'Nai B'rith Women and Americans for Democratic Action to the National Council of Senior Citizens, the National Organization for Women and the United Steel Workers. There were old, established organizations speaking for hundreds of thousands of members and newer, smaller, feminist organizations. They were brought together by growing concern that the conservative takeover in Washington combined with a deteriorating economy spells a real and present danger to the gains women made in the '70s.

There was some talk about the equal rights amendment, but not that much. These women already knew the arguments for ERA, they had heard them before, they'd lobbied for it before. This was not a crowd that was likely to go along with the argument that you can do away with sexual discrimination by changing individual laws. Barbara Mikulski (D-Md.), addressing a packed midday rally in the Cannon House Office Building, reinforced that point. "Can you imagine," she said, "if Abraham Lincoln had said to Harriet Tubman, we're going to have emancipation but not the proclamation -- we're going to do it plantation by plantation?"

Uppermost on the minds of the women who came to Washington were economic issues and the so-called Human Life Amendment, which is an anti-abortion amendment that protects the fetus from the moment of conception. Opponents say this means that some of the most effective means of contraception such as the intrauterine device, which prevents the fertilized egg from being imbedded in the uterine wall, would be illegal if the amendment is passed.

The idea of such an amendment getting anywhere in Congress seemed preposterous before the last election.The women gathered in the Caucus Room, however, understood its implications and listened grimly as Rep. Shirley Chisholm (D-N.Y.) told them that the antiabortion forces in Congress are talking about trying to get a discharge petition to bring the amendment out of committee and onto the House floor. "And I believe that if it reaches the floor it will pass," she said. She warned them that now is not a time for infighting within the women's movement, nor as she put it, is it a time for shrinking violets.

There weren't any on the Hill the other day. Gloria Steinem told the women that they were a tribute to their primary organizer -- Ronald Reagan. Not since the lobbying to get an extension of the Equal Rights Amendment has there been such a large, highly organized effort for women's rights on the Hill. Hearings on women's health issues and on economic issues were packed. Members of the Congresswomen's Caucus -- new members and old members, Republicans and Democrats -- called the hearings and sat in on them and participated in the rally. A delegation of women met with House Speaker Thomas P. O'Neill and Senate minority leader Robert Byrd.

Rep. Mary Rose Oakar (D-Ohio) introduced on the same day a five-bill package designed to modernize the Social Security system so that it reflects economic life in the 1980s, rather than the 1930s when Social Security was started. Three of her bills would implement the concept of earnings sharings, which means that the work of the homemaker would be recognized in the marriage and in the allocation of benefits. Benefits for widows, disabled homemakers and divorced women would be enhanced.

Older women are the fast-growing poverty group in America. Because of their work patterns and their dependency on husbands for Social Security benefits, women receive substantially less from the program than do men. While it may seem politically foolish to try to correct inequities in the system during an administration that is trying to hold down benefits, Oakar believes her timing may be just right. All the attention that's being given to beating up on the Social Security program could be turned around into looking at the whole system. "Let's make it a positive target to correct injustices that are neither beneficial to men or women," she said.

Whether that can happen will depend, at least in part, on how well women begin to understand the inequities in Social Security, and in how well they understand a lot of the other legislation that will come up on the Hill this session. Whether it is the Human Life Amendment or changes in the Social Security system or any of the other economic proposals that are going to be made, women are going to be affected perhaps as never before.

The women who lobbied Congress on Wednesday understood that. This was the first test of the women's movement's ability to turn out a crowd of committed lobbyists since the election. And if there is any one thing you could say about what happened Wednesday, it's that rumors of the demise of the women's movement have been greatly exaggerated.