The decision of Michigan Republicans to create what amounts to the earliest presidential primary in the nation has produced an explosion of political activists here operating in a financial shadow world at the edge of federal campaign law or claiming immunity from it altogether.

The three major prospective presidential candidates active here -- Vice President Bush, Rep. Jack Kemp (R-N.Y.) and the Rev. Marion G. (Pat) Robertson -- have set up almost identical organizations with headquarters operations and field staff assigned to congressional districts. Each, however, is using a different vehicle to raise and spend cash.

The vehicles, which finance efforts costing from $100,000 to $400,000, range from a "multicandidate" federal political action committee (PAC) to a charitable organization seeking tax-deductible status.

The central, if not exclusive, goal of all these organizations is to elect thousands of precinct delegates in the Aug. 5 Republican primary. These delegates, in one unusual twist of presidential politics, will ultimately determine who will represent Michigan as delegates to the 1988 presidential convention.

Leaders of the groups trying to elect precinct delegates maintain they are not bound by federal law governing presidential campaigns. That includes contribution limits, spending ceilings, and, in the case of the charitable organization, prohibitions on the receipt of money from corporations.

The Michigan Opportunity Society (MOS), the organization generally tied to the Kemp campaign, expects to spend at least $100,000 lining up people to run for precinct delegate in the August 1986 primary.

"There is no formal organization," Clark Durant III, head of MOS, said. "This is a movement whose leader is an idea, it's not any one of us. Each of us is a servant to the vision . . . We are a movement, not an organization."

In practical terms, that explanation translates into the assertion by Durant that MOS has no obligation to file reports with the Federal Election Commission listing the names of any of the more than 30 individuals who have given $70,000, or how the money is being spent.

"I don't think I have to register as a federal PAC since I am not involved in a federal election," Durant said. MOS may disclose its contributers to the state in late July, but, if it restricts its activities to supporting precinct delegate candidates, it will be under no obligation to do so under state law. Durant added that the question of disclosure to Michigan officials is "under review."

If the election were held today, everyone in MOS would vote for Kemp, according to Durant, who said that the group's major activity is to mobilize everyone who responds favorably to Kemp after he makes one of his frequent speeches here. But "I do not see myself as a Kemp for President operation," said Durant, who is also chairman of the Legal Services Corporation.

If the Kemp campaign -- or "vision" -- is using an unusual vehicle, Robertson, the conservative religious leader and head of the Christian Broadcast Network, is channeling large sums of money into Michigan through an educational charity, the Freedom Council.

Dick Minard, the executive director of the Freedom Council, said that $35,000 to $40,000 is going into Michigan each month in a major drive to find people to run for precinct delegate.

To run the Michican operation, the Freedom Council hired Marlene Elwell, a skilled political organizer from the 1970s antiabortion movement who moved into Republican Party politics in the 1980s. The Freedom Council has set up a structure almost identical to MOS and the PAC affliliated with Bush, the Fund for America's Future. Elwell runs a small headquarters staff, while a field operation has been assigned to the state's 18 congressional districts, one person for every two districts.

Elwell says that the purpose of the Freedom Council is to encourage political participation in both parties by members of the Christian community:

"I felt that in 1984, an area that was very lacking was the Christian community. It was totally ignorant of the political process. Often I found a feeling that they shouldn't get involved in it, they should stay home and pray while everybody else was out working."

Elwell said that the Freedom Council is entirely separate from any potential Robertson candidacy. "If he does or doesn't run, this is something I want to go on into the 1990s," she said. "The Freedom Council will go on past 1988. The Michigan Opportunity Society -- the Kemp program for Michigan -- has been organized just for the purpose of getting delegates for Kemp."

In support of her argument, Elwell said "We have fundamentalist Baptists who would take their congregations 100 miles away from a Pat Robertson a Charismatic , but they have the values that we are looking for. So we say, fine, run."

In the privately expressed view of Kemp and Bush supporters, however, the Freedom Council is politicizing a community that would provide a natural base for a Robertson candidacy. The council has sponsored three visits into this key presidential state by Robertson -- the latest was a two-day stop-over at the end of February.

The Bush PAC is disclosing contributors and expenditures. Its best break to date has been persuading the FEC to permit the group to invest heavily in Michigan without falling under presidential election spending requirements.

Despite the fact that in Michigan, every minor decision made by Republican Party officials is viewed in terms of how it will benefit the campaigns of Bush, Kemp, Robertson and other potential competitors for the presidential nomination, the FEC voted to exempt precinct delegate recruitment and support from restrictions applying to presidential campaigns.

Overruling the FEC's legal staff, who argued that the purpose of the Michigan precinct delegate contest is to influence the presidential nomination, the FEC voted 4 to 2 to allow the Bush PAC to spend money in Michigan without the presidential campaign restrictions. The advantage Bush gains from this ruling is a clear path for his massive fund-raising machine. The vice president's PAC has received well over $4 million in less than a year -- in the key battle in Michigan.

In addition, the favorable ruling means that money received by the Bush PAC will not count against the overall primary spending limit imposed on presidential candidates, which in 1984 was $20 million apiece.

Prospective Republican presidential candidates face what is likely to become the longest, most expensive campaign in history, and all are seeking ways to raise and spend money without falling under spending ceilings.

Along the same lines, the FEC ruling means that Bush will be able to continue financing activities through the Fund for America's Future which can take contributions of as much as $5,000 every year from an individual, instead of the $1,000 limit that applies to a presidential campaign committee.

Meanwhile, the Bush PAC has been conducting an intense drive in Michigan to get local Republicans to join the PAC's steering committee, a step that does not require endorsing Bush as a presidential candidate.

To date, the Bush PAC has signed up more than 1,400 GOP officials, including 500 to 800 precinct delegates, according to Ken Connolly, executive director of their Michigan operation.

Connolly says that the purpose of the Bush PAC is not to promote Bush's candidacy, but to support GOP party-building activities in Michigan. "Our organizational work is to strengthen the party. We encourage precinct participation and the way to do that is to become a precinct delegate."

L. Brooks Patterson, one of four Michigan cochairmen of the Fund for America's Future was more direct about the fund's goals: "The Bush PAC will deliver a plurality plus one of the delegates. Anything above that will be frosting. I'm targeting a win by one delegate. That's my job."