The Supreme Court divided evenly yesterday over the constitutionality of an Oklahoma law that allowed school boards to fire teachers who publicly advocated or promoted homosexuality.

The 4-to-4 split, made possible because Justice Lewis F. Powell Jr. did not hear oral argument or participate in the case, automatically upholds a lower federal appeals court ruling that threw out part of the law as a violation of teachers' rights to freedom of speech.

The tie, announced in a one-sentence statement that did not indicate how the justices voted, does not set a national precedent and left both sides claiming victory.

Powell, who returned to the bench Monday, missed oral argument in 56 cases following surgery for prostate cancer in January.

His absence illustrates the significance of one justice's illness in a sharply divided court.

The eight remaining justices split in another case decided yesterday, leaving intact a New Mexico ruling that a motorist who caused an accident could be tried on separate charges in two different courts. The case is Fugate v. New Mexico.

The court on Monday ordered three other cases argued earlier this term to be reargued next month.

No reasons were given but the likelihood is that the court, which heard the cases in Powell's absence, is closely divided in those cases as well.

The remaining eight justices gave no indication why they decided that some cases should be reargued while others should be disposed of on a tie vote.

Knowledgeable court observers said yesterday that the justices may see more legal significance in the life insurance, taxation and labor cases to be reargued than in the cases ruled on yesterday.

One observer said that, after oral argument, some of the justices may have decided for one reason or another that the cases should not have been granted a hearing in the first place.

The tie vote rids the court of the cases without creating new law while the reargued cases, with Powell back, should lead to nationally binding rulings.

The homosexual advocacy case involved a 1978 Oklahoma law, which had never been used, that provides for the firing of any teacher who "advocates homosexual activity in a manner that creates a substantial risk that such conduct will come to the attention of school children or school employes."

The National Gay Task Force challenged the law, saying it was too broad and would inhibit teachers from expressing their views on homosexuality.

Harvard Law professor Laurence Tribe, who argued the case for the National Gay Task Force, said that while the ruling was not definitive, yesterday's action indicated at least that four justices were willing to hold such statutes unconstitutional. "It is a signal that there will be no green light from this court for laws silencing" speech about homosexuality, he said.

Tribe said that other portions of the law, which prohibit teachers from soliciting or imposing homosexuality in the classroom, remain in effect.

But Larry Lewis, an attorney for the Oklahoma City Board of Education, said, "We also consider it a victory. I'm sure what will happen is that the legislature will seek to pass a new law," that will be tailored to meet the appeals court's objections. The case is The Board of Education of the City of Oklahoma City v. The National Gay Task Force.

In other action yesterday, the court:

* Ruled 8 to 0 that a defendant cannot be convicted twice for possession of a firearm and receiving that same firearm. The case is Ball v. U.S.

* Ruled 5 to 4 that Alabama cannot give preferential tax treatment to in-state insurance companies, a decision that could limit state programs to encourage local businesses.