The Supreme Court yesterday ruled that courts may not interfere with the process by which the political parties choose their presidential candidates.

The ruling has the effect of eliminating "open primaries," in which non-Democrats help select Democratic Party delegates, in Wisconsin, Montana and Michigan.

Its more far-reaching impact, however, will probably be to strengthen the hand of party officials who want to cut down drastically on the growing number of primary elections and stop states from jockeying on the timing of primaries.

Under yesterday's opinion, the states can hold primaries as they please. But the parties can now threaten to render them meaningless by refusing to seat the delegates selected without fear of court challenges.

The court ruled in a similiar case in 1975 that political parties are private organizations with rights of "free association" protected under the First Amendment.

Yesterday, citing that ruling, the justices reversed a Wisconsin Supreme Court decision ordering the national Democratic Party to seat at the 1980 convention a Wisconsin delegation selected through an open primary in violation of party rules.

"A political party's choice among the various ways of determining the makeup of a state's delegation to the party's national convention is protected by the Constitution," Justice Potter Stewart wrote for the majority. "And as is true of all expressions of First Amendment freedoms, the courts may not interfere on the ground that they view a particular expression as unwise or irrational." Wisconsin's open presidential preference primary, which was adopted in 1903 as part of that state's Progressive Party movement to open up the selection process, is famous for crossover voting. Anyone, including Republicans and independents, can vote in the April Democratic primary.

Most other states require primary voters to declare their party affiliation.

Convention delegates are selected in caucuses in Wisconsin, but they must vote according to the preferences expressed in the primaries.

The system existed unmolested until 1976, when the national Democratic Party enacted a rule restricting participation in the delegate selection process to "Democratic voters who publicly declare their party preference and have that preference publicly recorded."

The change was prompted by a concern that rank-and-file Democrats were underrepresented at the convention. In 1976, the party made exception for states that could not secure legislative change in their primary systems. But in 1980, the exception was withdrawn and the rule enforced.

The party refused to seat the Wisconsin delegation because it was bound by the preference primary results. The state appealed, obtained the Wisconsin court order, and the delegation was seated while the appeals process began.

Yesterday, the court said that the Wisconsin Supreme Court had no authority to issue its order. Wisconsin is free to make its own rules for holding primary elections, the justices said, but the national Democratic Party is a "compelling" constitutional reason to the contrary.

Wisconsin Democratic Party Chairman Joe Checota said yesterday that the "open primary as it has existed in Wisconsin for 75 years is dead." He said he would try to convince current party leaders to modify the rule. Failing that, state party officials and legislators will begin designing a new system, he said.

Justice Lewis Powell wrote a dissent in which he was joined by Justices Harry Blackmun and William Rehnquist. They argued that the open primary law did not substantially infringe the party's First Amendment right of association and that it "promotes the free political activity of the citizens of Wisconsin."