The Senate yesterday broke a three-month filibuster against legislation that would take the federal government entirely out of the school-busing business and restrict the power of federal courts to issue busing orders as well.

By a 61 to 36 vote, one more than necessary, the Senate on its fifth try adopted a cloture motion ending a lonely filibuster by Lowell P. Weicker Jr. (R-Conn.) and a handful of other senators.

The Senate then approved a rider to a Justice Department authorization bill that would prevent federal courts from ordering busing to correct racial imbalance except in rare instances, and would allow the undoing of any existing court-ordered plan where students were bused more than five miles or 15 minutes from their homes. It would also forbid the Justice Department to take part in any court case involving busing.

But resolution of the matter is still in doubt. Before approving the rider, sponsored by J. Bennett Johnston (D-La.) and Jesse Helms (R-N.C.), the Senate agreed to delay action on the authorization bill, and Weicker vowed to resume his filibuster when debate resumes, probably in late October. "It has taken three months to get this far," he declared after the tension-packed cloture vote. "I can assure my colleagues it will take much more than three months to ever get to final passage."

"There's no doubt in my mind the Senate wants to pass this unconstitutional piece of legislation," Weicker later told reporters. "I can't win. But I win every day that I delay this malodorous meadow muffin from becoming law."

Johnston conceded it might be the end of the school year before the Senate approves his legislation. But he said the 61 votes on the cloture motion demonstrated the overwhelming support for the measure.

The House has also approved an anti-busing rider, but one less broad. It would restrict the Justice Department but not the courts.

The Senate adopted Johnston's amendment 60 to 36. Paul S. Sarbanes (D-Md.) and Charles McC. Mathias Jr. (R-Md.) voted against it and the cloture motion; John W. Warner (R-Va.) and Harry F. Byrd Jr. (Ind.-Va.) voted for both.

Arlen Specter (R-Pa.) charged that the Johnston amendment was an unconstitutional intrusion by the legislative branch of the government into affairs of the judiciary. "It poses a most serious threat to the authority, power and jurisdiction of the Supreme Court," he said.

The measure has been condemned by the American Bar Association, a host of legal scholars and almost all civil rights groups. Ralph Neas, director of the Leadership Council on Civil Rights, yesterday called it "the most pernicious anti-civil rights amendment ever to come to the Senate floor."

"This is not a busing amendment," he added. "It is an attempt to overrule a Supreme Court ruling by a majority vote on the Senate floor."

The Senate failed in four earlier attempts, the most recent last week by a 57-to-33 vote, to end the filibuster.

Majority Leader Howard H. Baker Jr. (R-Tenn.) said he will bring the entire authorization bill up sometime in late October.

The Senate then will also consider a related anti-busing amendment by Helms and a series of other amendments by other senators. This will provide Weicker at least three more attempts for a to filibuster: on the Helms amendment, final passage of the bill, and approval of a House-Senate conference report.