Overruling the objections of legal staff and two Democratic commissioners, the Federal Election Commission yesterday cleared the way for Vice President Bush to use his political action committee (PAC) to help elect precinct delegates in a Michigan primary next August.

The decision left Bush aides elated while angering officials of Common Cause, a self-styled reform group, and Democratic Commissioner Thomas E. Harris.

"If this decision had gone against us, we would have been all dressed up with no place to go," a Bush strategist said. "This makes our advantage an advantage." Bush's PAC, the Fund for America's Future, has raised $3.9 million, far more than any of the PACs of prospective competitors for the 1988 Republican presidential nomination.

In a bitter dissent, Harris wrote that the FEC "has, step by step, gotten itself into the absurd position that it refuses to acknowledge what everyone knows: that Vice President Bush is running for president and is financing his campaign through the Fund for America's Future . . . . This is ridiculous."

Common Cause President Fred Wertheimer said the decision is "absurd . . . The commission has opted for fanatasy over reality. The four members of the commission who supported this approach are apparently the only people in the country who don't understand what's going on here."

Bush, according to aides, has four full-time and nine part-time staff members working in Michigan. The primary there is widely accepted as the first test of the GOP presidential contest because the 8,000 to 10,000 precinct delegates elected in August will, in 1988, begin the process of selecting the Michigan delegates to the Republican National Convention.

The FEC ruling means that Bush and other candidates using PACs will be able to spend money in Michigan without it counting against presidential spending limits. In the 4-to-2 vote, the three GOP commissioners voted unanimously to allow Bush to use his PAC, and they were joined by Democratic Commissioner Danny L. McDonald. The two remaining Democrats, Harris and John W. McGarry, voted against the Bush PAC.