PONTIAC, MICH., JAN. 14 -- Vice President Bush tonight gained a potentially decisive lead in the battle for Michigan's 77 Republican convention delegates as supporters of Pat Robertson and Rep. Jack Kemp (R-N.Y.) stalked out of over 20 county conventions where party rules favored Bush.

Preliminary vote counts by the National Election Service gave Bush 65 percent of the delegates who, later this month, will determine the makeup of Michigan's delegation to the national GOP convention in New Orleans.

The Bush vote totals were skewed by the Kemp-Robertson walkouts and may be reduced by challenges expected at the Michigan state convention Jan. 29 and 30. But Bush's edge was large enough that even if all the challenges to his supporters are successful, he could still gain a working majority at the state meeting.

Across the state, 106 conventions involving more than 9,000 "precinct delegates" were held tonight. The precinct delegates elected 1,805 state convention delegates who two weeks from now will choose Michigan's 77-member delegation to New Orleans.

However, the Robertson-Kemp rump meetings, which selected separate slates of delegates to the state convention, appears to guarantee that well over a third of the 1,805 will be challenged and face a credentials fight.

In many areas, the Robertson-Kemp forces were helped by staffers from another contender -- Sen. Robert J. Dole (R-Kan.), who made little effort in Michigan. "We believe in fair play," Don Devine, a senior consultant to the Dole campaign, said with a smile as he helped orchestrate the walkout here.

The bitter contest has laid waste to one of the most effective state parties in the nation and turned internal GOP tensions between party regulars and evangelical Christians into an open wound.

Ben Waldman, a Robertson spokesman, said, "There is not one Robertson supporter in Michigan who would work for George Bush after this."

The formal selection process began in an August 1986 primary where the "precinct delegates" meeting tonight were selected. But the battleground quickly shifted to the 101-member state central committee, where an "anybody-but-Bush" alliance between Robertson and Kemp gained the upper hand. From there it went to the courts, where Bush has won four out of four lawsuits.

At the county gatherings tonight, the Robertson-Kemp forces were geared up to walk out in defiance of pro-Bush rules in as many as 30 locations.

"In some sections of the state, the inmates have taken over the asylum," declared L. Brooks Patterson, Oakland county prosecutor and a Bush supporter.

Bush's improved chances to win a plurality of the state's convention delegates were clearly reflected in his comments today and those of his major competitor, Robertson.

Michigan, Bush said, is "a key test of our campaign and those of Robertson and Kemp. It is vitally important for me and my campaign and the pursuit of this presidency to do the very best we can in Michigan." Politicians usually do not make this kind of statement unless they expect to win.

"The vice president's people have thrown that state {Michigan} into total chaos," Robertson said while campaigning in South Carolina. The final result "might not be decided until the convention {in August} in New Orleans," an aide said.

However, when Bush forces learned that the Robertson-Kemp alliance planned to use its control over the GOP central committee to set up a new system to challenge the credentials of delegates going to the state convention later this month, they lost much of their enthusiasm.

"Now we are not going to have a winner or loser in Grand Rapids," Patterson said. Noting that he expects the fight to go all the way to New Orleans, Patterson added, "I don't think the Michigan results will have any consequence. We are a nonentity. We have outsmarted ourselves."

In a meeting near Dearborn, Bush supporters brought copies of the death certificates of two pro-Kemp precinct delegates who died after the 1986 election. Bush strategists said they wanted to be sure Kemp and Robertson organizers didn't attempt to quietly substitute people to fill the seats.

The extraordinarily complex delegate selection system was originally designed to put Michigan on the political map by making the state the first in the nation to choose its delegation to the convention. Instead, it has provoked a debilitating Republican civil war that has severely undermined the prospects of state GOP candidates in 1988. "If we elect a statewide Republican before 2010, I will be surprised," a key Republican commented privately.

In addition, there is a strong likelihood that tonight's county conventions and the statewide convention at the end of the month will fail to produce clear-cut results. The loser, whether Bush or Robertson, is sure to continue to appeal in the courts and to contest the results in August in New Orleans.

For most of the 18 months of this contest, the Robertson-Kemp alliance has been able to use its control over the state party to repeatedly embarrass the vice president, who defeated President Reagan by a 2-to-1 margin in the 1980 primary here and began the fight for the 1988 delegates as the overwhelming favorite.

In recent months, however, Bush forces surprised the Kemp-Robertson alliance, outflanking them to use his influence over little-known county Republican executive committees to set up a gerrymandered system of selecting delegates to the statewide convention in Grand Rapids two weeks hence.