THE THOUSANDS of women who descended on Washington last weekend, urging Congress to give them more time to win ratification of the Equal Rights Amendment by the necessary 38 states, may have been making a mistake.

It is true, of course, that with the ratification drive currently three states short and with the 7-year ratification deadline up next March 22, the prospects for ERA are gloomy. But at this point it would perhaps be better if the deadline were not extended.

In part, this is because of immediate practical problems. Even in the unlikely event that Congress would pass a controversial extension of the deadline in an election year, chances are that it would do so only if it also allowed states that have approved ERA to rescind their votes.

This raises the possibility that ERA supporters might lose more votes than they could gain by an extension. It also means the issue might be tied up for years in the courts, since the legality of rescission has never been tested.

In addition, ERA proponents, already on the defensive, would be burdened with another difficult charge to defend: that they unfairly changed the rules of the game. The charge is already emerging, even among some who are sympathetic to the women's movement. As political consultant Curtis Gans recently wrote. "There is something fundamentally incongruous when a movement committed to the principle of political equality seeks unequal treatment from the law."

But perhaps most important, what would result if the deadline is not extended is a reassessment by the women's movement of where it's been, where it's going, and what went wrong.

LOSS OF ERA for now would be tragic. Pressures on businesses, unions, judges and politicians to continue gains for women would likely be eased. The country would have to face the fact of telling half its citizens that the Declaration of Independence's phrase, "all men are created equal," does not mean them.

But that certainly would not be the end of the issue. Women's leaders clearly are determined to press the matter, and they surely would start over to pass the amendment again in Congress.

That new beginning might be best. This is not only because it would make relatively little difference in the time which then would be needed for ratification by three-fourths of the states - the movement, after all, has been asking for seven more years - or that it would remove many other complications. It is also because it would force that badly needed reassessment of the movement's strategies.

For one thing, it seems clear that the movement needs to shift its emphasis from rhetoric - from marches and conferences and consciousness-raising - to expertise in gut-level politics. We know the issues, but we do not know how to translate them into political action.

This is not to point the finger of blame. For a movement that was "born again" only in the late 1960s, it has made incredible gains. Women have moved into jobs traditionally closed to them, from airline pilots to a women appointee to the Federal Reserve Board. They are entering schools of law and medicine at record rates, and they have won such discrimination suits as the landmark AT&T case.

Everything, however, is not roses. While more women are entering the work force then ever before, they are filling lower-paying jobs and, compared with the pay men receive, are actually losing ground. In 1971, women earned 63 cents for every dollar a man earned, but by 1975 this was down to 57 cents. The ERA's equal protection clause is necessary to insure a legal unbrella for further advances.

But if the ERA and the movement are to make further gains, involved women will have to take stock and change.

A MOVEMENT that tries to encompass a group so large as "women" has problems like no other organization, except perhaps a political party.

A political party to be viable must have a broad base, raise money, accentuate the issues of widest appeal and de-emphasize the negative. It must take the offensive as often as possible and avoid being trapped defending extremes or fighting large numbers of unwinnable battles. Until now, these were not principles the women's movement was forced to emphasize.

When the movement was reborn in the 1960s, nothing seemed to stand in its way. It touched a deep nerve in millions of American women, and they responded with a vehemence. By the mid-1970s, the leaders - Betty Friedan, Gloria Steinem and others - were familar faces, "women's lib" was part of the language, states were liberalizing abortion laws, corporate boards were looking for women to serve on them, and the ERA had passed Congress after 50 years.

But then younger, more radicial women came to prominence, women such as Karen DeCrow, who became head of the National Organization for Women. DeCrow announced that she would press for equal rights for lesbians.

The reaction set in. The right wing, personified by Phyllis Schlafly, began gathering the women who felt threatened with a loss of "rights" for wives and mothers or who dissented on the controversial issues of abortion or gay rights.

The reaction was normal and should have been expected. As Democratic Rep. Patricia Schroeder of Colorado remarks about congressional passage of ERA, it may have been "too easy." The women's movement was not used to fighting hard, only to winning.

Now the movement knows, as Eleanor Smeal, the housewife who currently heads NOW, says, that ERA is not an undeniable human right, "it's political issue."

Fighting it like a political issue requires two things. It requires the movement to make hard choices, and it requires it to admit mistakes.

ERA HAS basically been lost in the more conservative southern and western states. Doris Holmes, ERA director in Georgia, an unratified states, tried to tell the Houston conference last year why. She tried to explain that the movement in her state had an "albatross" around its neck in the gay rights issue. But she was booed and hissed, and a gay rights plank was passed.

Smeal admits that the plank makes ERA passage more difficult, but she says women must be for all human rights. "What is so threatening about sexual preference? If we haven't got our ideals, what have we got?" She considers backing off gay rights as selling out.

She is wrong. Important as the issue is, discrimination against homosexuals, which is discrimination against both men and women, is not central to the women's movement. Discrimination by race, class, religion, ethnicity and age are also important "human rights" issues, as are international tyranny and torture, but they, too, are not central to the women's movement. Backing off the politically costly gay rights issue would not be a sellout, any more than failing to concentrate on other human rights issues is a sellout.

On the contrary, it would be a politically wise step toward helping the millions of women, from secretaries to housewives to assembly-line workers to other working wives, who make up the movement's broad base. The danger is that they will drop out as the needs central to their lives - better birth-control alternatives, better day care, and economic protection and justice - are left unanswered.

Moving away from gay rights is one of those cold, difficult choices that must be made if women want to win their major battles. The problem, as the chairman of a state delegation at last year's Houston conference said, is that "You can't convince the liberals that the women's movement isn't strong enough to kill all the ills of society at once."

The movement is also not strong enough to even appear to exclude women who differ on the abortion issue.

The abortion fight is important, but it runs into religious and moral beliefs in addition to being a women's issue. Women who disagree on abortion should not have to feel like second-class members of the movement. The Republic Party evidently has lost members by making liberals and moderates feel like second-class party members and because of right-wing demands for purity on issues, such as the Panama Canal treaties, not central to its philosophy.

The women's movement must also review its political tactics. A weary Chicago legislator who had voted consistently for ERA says the stridency on both sides was wearing him down. "To tell you the truth, I would have promised my vote to the first side which offered not to yell at me anymore," he remarks only half facetiously.

One of the most ill-conceived tactics is the decision not to hold conventions in states that haven't ratified ERA. It is big cities that suffer the loss of trade from this boycott. Yet ERA gets most of its support from big city legislators.

Florida is a classic case. The kingpin of the Florida senate and the leading ERA foe, Dempsey Barron, is an arch-conservative Democrat from the Florida panhandle. But it is Miami that is hurt by the boycott in Florida. Barron, as is typical of many rural state legislators, views the city as a blot on the landscape. Boycotting Miami could not please him more. The basic tenet of political strategy is to hurt your enemies, not your friends.

A women delegate at the Houston conference last year, watching for a while as the movement leaders - Friedan, Steinem, Bella Abzug - spoke, summed up the needs of the movement today. "I'd trade them all for one female Lyndon Johnson," she said.