Washington — After months of holding back the contentious social issues, the dam has finally cracked in the US Senate.
With a comfortable 58-to-32 margin, the upper chamber last week approved the most stringent antibusing measure ever passed by either house. It would forbid judges to order school busing beyond 5 miles or 15 minutes and possibly reopen hundreds of school desegregation cases settled long ago.
Attached as a ''rider'' to a spending bill, the antibusing amendment still faces high hurdles before it can be made law. The Senate will vote this week on limiting debate on the bill itself, and final passage will be delayed, probably until March.
The antibusing measure is only the first of a stream of proposals expected on the Senate floor this session to curb federal courts in the social areas. Next in line:
* School prayer. Sen. Jesse Helms (R) of North Carolina, who sponsored the antibusing amendment, has proposed legislation to per-mit states to authorize voluntary prayers in schools. His proposal would strip federal courts of the power to intervene.
* Abortion. The Senate Judiciary Committee will soon vote on whether to back the so-called Human Life Bill, also sponsored by Senator Helms, which would define a fetus as a person, or to support an antiabortion constitutional amendment proposed by Sen. Orrin G. Hatch (R) of Utah. The amendment appears to be winning.
Despite all the signs of activity, many observers on Capitol Hill and lawmakers themselves doubt that any of the efforts in these controversial areas will see final enactment this year. In fact, some opponents of the court-curbing efforts say they are undismayed over the antibusing Senate vote.
''Court-stripping legislation has always been well received in the Senate,'' says Robert W. Kastenmeier (D) of Wisconsin, chairman of the House subcommittee on the courts. ''I think the House is quite a different matter.''
The Senate's proposed busing ban, attached to a Department of Justice authorization bill, goes far beyond a House-passed measure, and a House-Senate conference will have to approve it. Mr. Kastenmeier, an opponent of limiting court jurisdiction, says that most of the House members of the conference would oppose it.
Since the Democratic, mostly liberal, House leadership will pick many of the conferees, the busing ban appears to have little chance of survival. Moreover, the bill it is attached to must still face the so-far unflappable Sen. Lowell P. Weicker Jr. (R) of Connecticut, who has been leading a filibuster against it. He has already filed several hundred amendments to slow up the final vote.
Opponents of the busing ban also take comfort in the fact that the Senate measure, jointly sponsored by Helms and Sen. J. Bennett Johnston Jr. (D) of Louisiana, would be only temporary. Since it is an amendment to a one-year Department of Justice authorization bill, the ban would expire next October and have to be reenacted.
''The Johnston amendment is a temporary measure,'' says a staff lawyer for Senator Hatch. Senators Hatch and John P. East (R) of North Carolina are negotiating on a bill to forbid busing as well as pupil assignments for desegregation purposes, permanently.
John Shattuck, Washington director of the American Civil Liberties Union, calls the antibusing vote last week a ''severe blow to the independence of the federal courts.'' However, he also sees little chance for completing major new laws on social issues this year, despite more than 20 bills already filed.