LANSING, MICH., SEPT. 15 -- The Michigan Republican Party tonight dealt another setback to Vice President Bush's presidential bid, approving rules damaging Bush's chances of winning a majority of this state's 77 delegates to the 1988 convention.

Bush forces concede that the decision -- engineered by backers of Marion G. (Pat) Robertson and Rep. Jack Kemp (R-N.Y.) -- increases the likelihood that the vice president will lose when Michigan becomes the first state to select GOP delegates in January, despite the fact that he has poured more than $1 million into the state and has the overwhelming backing of the party's establishment.

"The Bush campaign is in serious shape, this is a very serious blow," David Walters, manager of Robertson's Michigan campaign, said after the 60-to-41 vote.

Mary Matalin, Midwest political director for the Bush campaign, said "it will be bad" if the Michigan party's decision survives a court challenge, which Bush forces announced immediately after the vote.

Rich Bond, Bush's deputy campaign manager, said, "If those folks want to fight all the way to {the convention in} New Orleans, we are ready."

The decision by the Michigan GOP State Central Committee represents the second victory within a week for Robertson, who won a symbolically important straw poll in Iowa on Saturday. Robertson and Kemp forces are privately discussing a strategy to allow Robertson to come in first among Michigan's convention delegates, with Kemp second -- although he did poorly in a vote here last year -- and Bush third. The strategy is designed to damage Bush's status as front-runner.

The key ruling taken by the Michigan GOP tonight limits participants in county and state conventions to be held next January to just over 9,000 "precinct delegates" elected in the state's August 1986 primary. It specifically bars an estimated 1,100 Republican Party nominees for city, state and county offices from automatically serving as precinct delegates without running for the posts.

The decision damages Bush's chances in this state, which he carried two to one over Ronald Reagan in the 1980 primary, because his strength lies among party regulars. Robertson brought thousands of outsiders who had never participated in GOP party fights into the precinct-delegate election process.

The Michigan Republican Party, with one of the most arcane and complex delegate-selection processes of any state in the nation, has produced the most divisive and hostile presidential fights so far in the battle for the 1988 nomination.

"The next thing they {the Robertson forces} are going to do is outlaw the word Republican," an angry Peter Secchia, the state's Republican national committeeman, declared as the state central committee moved toward barring the 1,100 party nominees. "It sounds to me like it's getting a lot like behind the Iron Curtain," he said, contending that the prohibition against the party's nominees will undermine the state party structure.

Dick Minard, who is running Kemp's Michigan campaign, said those charges reflect a "losing, desperate campaign. The Bush campaign lost in {the precinct-delegate} election in 1986; they are just trying to change the rules to salvage their campaign."

When the 9,000-plus precinct delegates were elected in August 1986 to start Michigan's presidential convention delegate process, Bush forces claimed they had won, with Robertson a strong second and Kemp a distant third. But in later county and state meetings of the precinct delegates, Robertson and Kemp backers joined forces in a demonstration of strength that, if it holds through next January, would ensure Bush's defeat in this state.