Vice President Bush, escalating his unannounced campaign for the presidency, announced formation yesterday of a "testing the waters" committee that will pump as much as $750,000 into the Aug. 5 Michigan Republican primary.

The announcement means that Bush will be spending $1 million or more in Michigan -- far more than his opponents, New York Rep. Jack Kemp and television evangelist Marion G. (Pat) Robertson, say they will spend -- in the first phase of an early, complex test of strength for the 1988 nomination.

In a separate development, Robertson backers filed to form a "Pat Robertson for President Draft Committee" yesterday at the Federal Election Commission. As long as the group acts independently, there are no spending restrictions and it may take unlimited contributions from corporations and individuals, according to FEC officials.

Bush's decision to form the special committee acknowledges the importance of the Michigan contest and moves him closer to an active presidential candidacy two years before the GOP convention.

In Michigan, Republican voters will select as many as 14,000 precinct delegates, a key step in a long process. Aides say Bush plans to endorse precinct delegate candidates in about 1,500 contests. The campaign will mail endorsements and distribute cards, brochures and other materials linking the candidates to the vice president.

Bush has already channeled $300,000 into Michigan through his political action committee, the Fund for America's Future. The PAC can support GOP candidates but cannot specifically further his bid.

The PAC will support precinct delegate candidates who do not face opposition and will encourage write-in campaigns in precincts where no one filed.

Marlin Fitzwater, Bush's press secretary, indirectly criticized the financing mechanisms used by Robertson and Kemp. "We want to appear to be taking the high road, especially when you consider some of the other efforts out there . . . ," he said. "It's to our benefit to make the contrast as stark as possible."

The Kemp drive in Michigan is being financed by the Michigan Opportunity Society. Clark Durant, who runs MOS, said it does not have to report contributions and expenditures because it is not a Kemp-for-president committee.

He said, however, that he expects MOS-backed precinct delegate candidates to "ultimately get on board when Jack Kemp gets the nomination." MOS has spent about $150,000 to date, he said.

In a more controversial strategy, most of the Robertson delegate candidates have been recruited by the Freedom Council, a tax-exempt organization founded by Robertson that can take unlimited contributions from individuals and corporations and is not required to disclose its activities. The Freedom Council's budget for Michigan is about $400,000, according to officials.

Bush said in a statement that he wants "to ensure that the political activity on behalf of delegates, and its financing, complies with all of the federal election laws." The exploratory committee "will allow me to endorse contested candidates and provide them support."

The money raised by the exploratory committee will count against state and national primary spending limits. In 1984 the ceiling was $24 million and in 1988 it will be about $26 million.

Donors are being asked to give no more than $750. This would, under the law, permit them to give another $250 after Jan. 1, when the contributions would qualify for federal matching funds.

Since the May 27 filing deadline for precinct delegates, officials of the Bush campaign, facing the Robertson threat, have reorganized the operation. They have brought in John Long, director of the state senate GOP caucus, to run daily activities, and former Republican National Committee political director Rich Bond to develop strategy.

The Robertson presidential draft committee will be run by Rob Flowe, a former official of the Freedom Council. Shepherd Smith, a specialist in direct mail and fund-raising whose companies were employed by the council, will be a consultant to the committee.