Treasury Secretary James A. Baker III, surprising some Republican insiders, met privately today with leaders of Vice President Bush's fledgling 1988 presidential campaign organization and gave a speech to a state party function on a trip partly financed by Bush's political action committee.

Baker said the trip, his first as treasury secretary under the sponsorship of a potential presidential candidate's PAC, posed "no conflicts" with his official duties and did not require any clearance from the White House.

"My longtime association with George Bush is no secret," said Baker, who has known the vice president for 30 years and who managed his 1980 presidential bid. "There's no [presidential] campaign yet . . . . It's not unreasonable to expect a Cabinet secretary to assist state committees and PACs organized to assist other candidates. Frankly, I don't see any problem with it."

However, some other Republicans expressed mild surprise at the overtly pro-Bush nature of the Baker visit. Most said they had no idea how the trip was financed.

"I would think he would be more circumspect," said Robert Heckman, chairman of the Fund for a Conservative Majority and an active supporter of Rep. Jack Kemp (R-N.Y.), another prospective candidate.

Heckman noted that as treasury secretary, Baker must work with two of Bush's potential rivals in 1988 -- Kemp and Senate Majority Leader Robert J. Dole (R-Kan.) -- to seek passage of tax revision and other administration legislation. "It surprises me he is getting out front this early," he said.

Baker met privately with Robert Teeter, a pollster and strategist who has worked for Bush and expects to do so again; state Senate Majority Leader John Engler, the highest ranking state official to announce publicly his support for Bush, and a cadre of other Michigan Bush supporters.

Baker's trip, which included a speech in Chicago Friday night to a party fund-raiser, was financed by the Republican National Committee, the Michigan Republican Party and the Fund for America's Future, Bush's PAC.

As Baker noted, the Bush PAC distributes funds to other GOP candidates for state and local offices. But such PACs also allow a presidential hopeful to put together a skeleton campaign organization long before officially entering the race. All the GOP's potential 1988 candidates have similar PACs.

Baker said there is no White House policy on the involvement of Cabinet members in the early politicking for 1988. He also noted he made an appearance last year for Kemp's PAC. Many here doubt, however, that he will do another for Kemp now that the 1988 race is beginning to take shape.

In Michigan, early organizing for 1988 has taken on special intensity. This state has adopted a presidential nomination process that starts next August -- a full two years ahead of the 1988 convention -- with the election of about 10,000 GOP precinct delegates. Those delegates will elect county and state delegates who in early 1988 will elect national-convention delegates.

Michigan, as a result, has jumped to the head of the calendar and hopes to attract more early attention from GOP hopefuls than perennial early birds Iowa and New Hampshire. That has already begun to happen. Both Kemp and Dole attended this weekend's conference; it was Kemp's fifth trip to the state this year, a spokesman said.

Bush strategists said he skipped the event because of scheduling, and because some of his Michigan leaders are afraid heavy early organizing will divert attention from state gubernatorial and legislative races next year.