Seven years after it hurst onto the seene as the nation's number one women's issue, the drive for the Equal Rights Amendment is dead in the water, three states short of ratification, with chances for approval increasingly bleak.

Its opponents, heady with real or imagined success, have scheduled a "victory celebration" at the Shoreham Hotel for tonight, the original deadline for approving the amendment.

"We've won," says Phyllis Schlafly, the self-appointed head of the stop-ERA drive. "When you win, you celebrate. It's an anniversary of historic proportions."

Schlafly overstates the care. Since Congress extended the original period for ratification last year to June 30, 1980, the battle for ERA is not over.

But there is a decided air of pessimism among many of its staunchest supporters.

"Personally, I don't think we'll pick up a single state with the extension." says Alice Kinkead, ERP director for the League of Women Voters. "If you look at all the trends, there's been an erosion of support."

Earlier this year, ERA supporters had hoped to reverse the momentum on the issue by scoring as many as three victories by early spring, making the amendment guaranteeing equal treatment for women a reality. But a well-financed lobbying drive failed this winter in three key states -- North Carlina, Illinois and Oklahoma -- and has only a slim chance of success in a fourth, Florida, where the legislature doesn't convene until April 3.

"We all hoped we'd pick up the four states, or at least one or two of them," says Jane McMichael, executive director of the National Women's Political Caucus. "There's no question that from this point out it's going to be very, very difficult."

To date, 35 of the 38 states needed to make it part of the Constitution have retified the ERA. And only one state, Indiana. has approved the amendment since 1977.

Meanwhile, four state legislatures -- Nebraska, Tennessee, Idaho and Kentucky, where the measure was vetoed -- have voted to withdraw their support for ERA, and the South Dakota Legislature has voted to declare its approval "null and void" after today.

Measures either to rescind or declare earlier approvals null and void have been introduced in seven other states. And ERA opponents in Washington state have said they will file suit in the state supreme court Friday contending the state's ratification resolution is no longer valid.

The setbacks have come at a time when ERA has become almost an establishment issue, supported by both major political parties, organized labor and, according to opinion polls, a majority of the American people.

But in state legislatures, the battleground where ERA will live or die, the amendment has become an extremely emotional issue, pitting urban against rural interests and liberals against conservatives.

It has escalated into one of those rare symoblic issues, representing conflicting goals and life-styles. Its supporters see it as a simple declaration that women are equal to men. Its opponents, including many women, see it as a symbol of permissiveness in society, women's liberation and a deterioration of traditional values.

In contrast to the early 1970s, when ERA passed many legislatures with little debate, it now becomes bogged down in divisive exchanges every time it comes up. And ERA opponents, frequently aided by fundamentalist religious groups, have mounted effective lobbying efforts.

"The states that passed ERA didn't study it, they didn't hold hearings," says ERA opponent Schlafly. "Any time equal time is given, we win."

ERA backers tend to blame their defeats on mossback state legislative leaders and the male-dominated political system.

"We're praying for key retirements," says Sheila Greenwald, director of ERA-America, a national corrdinating group."The political reality is that if we could remove the leadership of some legislatures the ERA would sail through without any trouble."

During the 18976 and 1978 elections. ERA backers successfully targeted a handful of legislators for defeat around the country in a show of muscle. And they plan to intensify this effort in the 1979 and 1980 state elections.

Some spokesmen, however, say that it will be next to impossible to defeat enough ERA opponents to change the complexion of enough legislatures to make a difference. "There are just too many seats to change," says Kinkead of the League of Women Voters. "You'd have to change the whole Nevada Legislature, for instance. The same is true on Arizona, Mississippi and several other states."

This year ERA was the victim of hardball politics as much as anything. Its supporters let it die in committee in North Carolina after they decided they didn't have enough votes to pass it in the state senate, despite intensive lobbying by Gov. James Hunt.

It died in Oklahoma when supporters couldn't muster enough votes to pass either house of the legislature. It died in Illinois on Valentine's Day, when an effort failed to reduce the number of votes needed to ratify a constitutional amendment there from three-fifths to a simple majority.

The only state where ERA is still alive this year is Florida. And it's just barely alive. Supporters there claim enough votes to win in the house, but they are deadlocked, 20 to 20, in the state senate, with little sign of movement.

"We're in a day-to-day situation," says Sen. Jack Gordon, and ERA sponsor. "It's a question whether the extension will cost us any votes. So far it hasn't, but we're afraid it might give a number of people another excuse to be against us."