Television evangelist Marion G. (Pat) Robertson put his presidential campaign on the air tonight, spending $100,000 to stage a political rally and televise it statewide via satellite.

Robertson, president of the Christian Broadcasting Network (CBN) and host of "The 700 Club," a religious talk show, rented a section of Cobo Hall, the site of Ronald Reagan's 1980 Republican presidential nomination, to highlight his exploratory bid for the 1988 GOP nomination and to demonstrate the political muscle of the Christian community that he is seeking to mobilize behind his campaign.

He drew 3,500 cheering supporters to the main gathering, and told them that "Christian people are saying we are going to make a difference. We are going to change things in Michigan . . . . Michigan will become the first state to be saying who the Republican nominee [in 1988] will be."

The rally was televised at gatherings in 10 other cities and five churches in the state.

Robertson, who is seeking to line up people to run for precinct delegate spots in an Aug. 5 election, said success in Michigan "will send a message to other Christians, other evangelicals . . . that [if] Michigan can do it, we can too."

After the rally, several people were signing up to run for precinct delegate.

Robertson was introduced tonight by Beverly LaHaye, who heads one of the largest conservative Christian women's groups in the country, the Concerned Women for America. LaHaye warned that "unless concerned Christians enter into the mainstream . . . , America will degenerate." She also told the group that "in God's hands, we can become the thunder and lightning."

At the close of the rally, Robertson brought the applauding group to its feet when he replied to a question about running for president by asking the crowd: "Should I do it?" The answer was a collectively roared "Yes."

Dick Minard, the national chairman of the Freedom Council, a tax-exempt group closely tied to Robertson, claimed his organization will line up 7,000 to 8,000 people to run for precinct delegate in the August election. That contest, coming 27 months before the 1988 general election, will serve as the earliest test of prospective GOP presidential candidates.

The August ballot does not identify the presidential preference of the candidates for delegate, nor are those who get elected obligated to stick with any candidate through the four stages of the process that will culminate in 1988. Nonetheless, several prospective presidential candidates are making major efforts to organize here.

Robertson plans to spend $300,000 to $400,000 in Michigan by the end of this month, more than twice the amount targeted by his two major competitors: Vice President Bush and Rep. Jack Kemp (R-N.Y.), who each plan to spend about $150,000.

Aides to Bush and Kemp said that lining up 7,000 to 8,000 precinct delegate candidates would represent an extraordinary demonstration of power by the Christian right within the Republican Party. However, supporters of both men question whether the Freedom Council can find that many candidates.

"They are not going to be able to file that many," said Bill Phillips, director of Bush's political action committee (PAC), the Fund for America's Future. "It's just not realistic."

Phillips said the Bush PAC, which has a staff of about 14 in Michigan, has commitments to run for precinct delegate from about 3,000 people, though he said he is not sure that all will follow through. "Democracy is a system of actions, not intentions," he said.

Another Bush supporter said that the precinct delegate drive amounts to a massive petition drive: in order to get on the ballot, each candidate must file a petition with 15 to 20 names of residents of the precinct.

"What that means is that for every 1,000 delegate candidates, you need 20,000 signatures. That's murder to get," he said. It would require 120,000 to 160,000 signatures to meet the legal requirements for 8,000 precinct delegate candidates.

In Iowa, many newly politicized evangelical Christians recently demonstrated the power to control the Republican Party in organizing caucuses in the Des Moines area. Iowa is one of the three most important states in the early jockeying for the 1988 GOP presidential nomination; the other two are Michigan and New Hampshire.

The filing process for precinct delegate, which has a May 27 deadline, will be as important as the August election, if not more so, according to political observers. Because interest in the race is so low, they say, filing is often tantamount to victory.