There is only one way that anybody, past or present, ever took a seat in the House of Representatives: by running for it, in a public election, and winning it. There has always been an alternative route to the Senate. A friendly governor, with a vacancy to fill, can still appoint somebody to be a senator. But only real voters, in an actual election, can make anybody a representative.

This may help to explain why no single event, outside of their own reelection campaigns, so engages the attention of incumbent House members as a special House election does. In the spring of 1974, upset Democratic victories in Grand Rapids and Cincinnati special elections persuaded a lot of House members, of both parties, that the presidency of Richard Nixon was doomed.

Nobody was predicting such a fate, last week, for the Reagan presidency even after the Democrats took a Mississippi House seat away from the Republicans. Still, the Democrats in Washington were smiling and sounding a lot less scared than they had been about 1982 and the Reagan magic. The combined House Democratic leadership was all over the Mississippi winner, Rep. Wayne Dowdy, like a cheap suit.

The sad and stupid part, for the Democrats, is that the Mississippi upset should have -- and almost surely could have -- been the second Democratic victory in a Republican House district in just 12 days.

On June 25, one day before the House vote on the Reagan budget, Ohio Democratic state Rep. Dale Locker came within 374 votes, out of more than 83,000 cast, of winning a congressional district that had not elected a Democrat since FDR's 1936 landslide. The district that is probably the most Republican in Ohio gave George McGovern 29 percent of its votes in 1972 and Jimmy Carter 30 percent in 1980.

Democrat Locker's $70,000 campaign budget, which left him outspent 3 to 1 by his Republican conqueror, did not include a single dollar from the Democratic National Committee. There is an explanation, but no excuse.

Last summer, at the Democratic convention in New York, the delegates adopted a loyalty oath -- the party's very first -- on the Equal Rights Amendment. From that moment forward, no opposing arguments or positions were to be respected or tolerated on the ERA. Never mind that Ohio had ratified the amendment on Feb. 7, 1974. Ignore the fact that ERA is not before the Congress. Deny the fact that ERA is not going to be ratified. Instead, cut off any help to a Democratic candidate running in a conservative Ohio district against a Reagan Republican. Punish him for his heresy on ERA.

It is not difficult to imagine what the mood of the House would have been on June 26, 1981, if Dale Locker had won the day before. Almost surely, enough wavering Democrats and wavering Republicans would have wavered away from the White House to change the six-vote margin. The result would have confirmed the president's slippage in the Gallup poll. The Mississippi results, less than two weeks after the Ohio "upset," would have probably left the administration "in some disarray" and facing its "first political crisis."

But of course that did not happen. One reason it did not happen was that a group of people, a militant minority, used the Democratic National Convention as an organizational imperative for their single-issue politics. They chose to hold the party hostage, because they knew the party leadership would do almost anything to avoid a televised brawl.They made their own non-negotiable demands on ERA. And the Democratic Party carved. The militant feminists demonstrated to their membership and to others that placing your cause on the nominating a president or any other political activity.

The Democrats should have learned in New York and have to realize, after the Ohio special election, that sometimes there is a larger cost than a "televised brawl."

Last weekend, the National Women's Political Caucus held its 10th annual meeting in Albuquerque. There, much concern was expressed about the Reagan budget cuts, which were viewed by those in attendance as particularly damaging to women and children. All but 29 House Democrats had voted against those Reagan budget cuts, while all but two House Republicans were loyal to their president on the key vote. Apparently, no reservations were expressed in Albuquerque over the Democratic loyalty oath, which helped to ensure House passage of those budget cuts.

Whether those Reagan budget cuts will actually damage women and children and others of little influence and less affluence will probably be known before next Christmas. If the cuts do hurt, the victims will have paid the price in 1981 for the Democrats' collective lack of courage in 1980 at the New York convention.