Washington — After waiting for more than a year, the abortion controversy is about to face a major showdown on Capitol Hill. The result could determine a major shift in direction for the nation -- either toward restricting or reaffirming abortion rights as set forth by the Supreme Court.
Brushed aside while Congress attended to the ailing economy, the issue can now wait no longer. Senate majority leader Howard H. Baker Jr. (R) of Tennessee next week delivers on his long-held promise to give abortion foes time on the floor.
It will come as part of the debate over raising the federal debt limit, which must be approved to keep the government from shutting down. An abortion measure could be attached to the debt limit bill.
In the debate expected to begin Aug. 17 the Senate will consider two of the most stringent anti-abortion measures ever proposed:
* Sen. Jesse Helms (R) of North Carolina presents his so-called human life bill, in which Congress would proclaim that ''the life of each human being begins at conception.'' If passed, it would open up the possibility of giving unborn babies full legal status and permit a raft of new anti-abortion legislation.
* Sen. Orrin G. Hatch (R) of Utah, meanwhile, is pressing for his ''federalism'' amendment to the Constitution, which would empower states to restrict abortion.
Either measure would attempt to reverse the 1973 Supreme Court ruling which articulated abortion rights and set off a backlash that has grown into a powerful political movement. Already the cause, symbolized by the red rose that its supporters wear, has won over the President and proved its clout in Congress. By increasing majorities, both houses have consistently voted to cut federal money for abortions.
But the two Senate proposals go much further, since they would cut into the basic right to choose abortion. As the vote nears, both sides say the vote will be close, but the pro-choice advocates are giving the most optimistic predictions.
''We will win decisively,'' maintains Nanette Falkenberg, executive director of the National Abortion Rights Action League (NARAL), leader of the pro-choice forces. ''This debate is a question of whether women can have abortions at all. It's not a funding issue. It's a clear question of whether to uphold the 1973 Supreme Court decision.''
Her group has counted enough votes to beat either the Hatch or Helms proposal , she says.
Senate sources have confirmed that the pro-choice side has an edge, especially on the constitutional amendment, which would require a two-thirds majority. Even if approved, the Hatch amendment has almost no chance of coming to the House floor this session.
''The Hatch amendment has 50 votes, no more, no less,'' says John Mackey, chief lobbyist for the Ad Hoc Committee in Defense of Life. He says that ''all of the pro-life groups are united behind the Helms bill'' because it is the fastest way to curb abortions.
Mr. Mackey concedes that the Helms bill will be a ''tough vote.'' Like others in his movement, he is pinning hopes on support from President Reagan.
''The President has spoken out time and again'' against abortion, says Mackey. ''He and his administration have a lot riding on this debate.''
Norman B. Bendroth, spokesman for the evangelical Christian Action Council, notes that only weeks ago President Reagan sent a sympathetic video message to the National Right to Life convention. ''It will be interesting to see if he lobbies as hard for the Helms bill as he did for the AWACS sale (to Saudi Arabia) or his tax package.''
Although predicting defeat of the human life bill, NARAL's Falkenberg says that if she is wrong, the result could be ''devastating. The statement that life begins at conception, that Congress could legislate on something like that, is ludicrous,'' she says.
While a victory for abortion foes could give a boost to their campaign, the Helms proposal would still face a rocky road on the way to becoming law. It would have to go to a House-Senate conference, where House members, picked by a pro-choice Democratic leadership, would be likely to strip off the measure from the debt limit bill.
A fallback strategy for the abortion foes appears to be attaching a less stringent measure to the bill. Oregon Sen. Mark O. Hatfield (R) has proposed a bill aimed chiefly at federal funding. However, following an hailstorm of criticism at home, Senator Hatfield first rewrote his bill to soften it and now says he will delay pushing for it.