The last Republican president tonight told the man who wants to be the next one that he should choose George Bush as a running mate.

In a one-hour private meeting, Gerald R. Ford made the case for Bush to Ronald Reagan, the man whom the Republican National Convention will nominate for president Wednesday night.

After the meeting, according to one source, Reagan said to another visitor:

"I'm getting the same advice from everyone -- that I ought to go with Bush."

Both Reagan and Ford seemed happy with the results of the meeting. A pro-Bush senior aide to Reagan said that Reagan and his staff were "tremendously pleased with the way it went," and described the meeting as "very good -- one of the best" in the series of meetings Reagan held during the day with various political leaders.

A Ford aide said the former president gave "a pro-and-con rundown, commenting on the strengths and weaknesses of the candidates." When Ford gave a similar public rundown on national television Sunday, it was highly favorable to Bush.

While there is still support at this convention for some alternative choices -- Rep. Jack F. Kemp of New York, Rep. Guy A. Vander Jagt of Michigan or former secretary of defense Donald H. Rumsfeld -- prominent conservatives swung to the advocacy of Bush today.

Five of six Republican leaders who met with Reagan at midday endorsed Bush, and these included such prominent conservatives as Sen. Strom Thurmond of South Carolina and Sen. John G. Tower of Texas.

Another leader present, Maryland Rep. Robert E. Bauman, said he preferred Kemp or Sen. Jesse A. Helms of North Carolina, but added that "I could live with Bush if I had to."

And Bush today picked up the support of both the Pennsylvania and Maryland delegations, and added key support in Reagan's highly conservative California delegation.

Reagan, however, has yet to indicate his choice, and he told several of those who called on him today that he has not yet made up his mind. That could happen at a midmorning meeting Wednesday at which Reagan and/or his principal aides will meet with prospective running mates or their aides.

Bush, the 56-year-old former U.N. ambassador and former Texas congressman, was Ford's chief recommendation to Reagan. Ford said before the meeting that he wanted to tell the former Calfornia governor: "You have at best a 50-50 chance of winning this election. If you believe otherwise, you are wrong. I have run against these guys [the Carter camp] and they are tough."

Ford's point, which a source said he made strongly in the private meeting with Reagan, was that the polls showing a runaway Reagan victory cannot be believed. Ford said Reagan needed a strong running mate to win the election, one who would unify the party, and the best choice was Bush.

A major point stressed by Ford, as it has been by Bush advocates within the Reagan camp, is that Reagan's opposition to the Equal Rights Amendment and the "pro-choice" position on abortion necessitate his naming a running mate who is more moderate on these issues.

Bush favors the Equal Rights Amendment and opposes a constitutional amendment limiting abortions to those necessary to save the life of the woman.

While Ford made these points strongly, according to a source, he did not say he would withhold support from the ticket if Reagan did not pick a running mate satisfactory to him -- as some had said before the meeting that Ford would do.

But his aides apparently succeeded in conveying to the Reagan camp the message that Ford would not -- under any circumstances -- take the No. 2 spot and create what Reagan chair man Sen. Paul D. Laxalt of Nevada had called "a dream ticket."

When Reagan emerged from the meeting, he said he had not asked Ford to run with him.

"I just wanted his consultation and help in the decision I have to make," Reagan said.

The only remaining problem for Bush appeared to be a lingering belief that Reagan either does not like him very much or does not consider him "presidential." Nancy Reagan also is reported to dislike Bush, but she denied this in an ABC-TV interview.

"Oh, no that's not true," she said. "That's just not true."

She also indicated that Bush's opposition to a constitutional amendment banning abortion would not rule him out.

"I don't think there is ever any person you're going to agree with 100 percent of the time," she said.

Reagan, meeting with a group of women who favor ERA, told them earlier in the day that Bush's support for ERA would not rule him off the ticket.

There was some rallying of conservative support during the day for Kemp and Vander Jagt. Ten conservative congressmen who endorsed Reagan at an early date discussed the entire field with him, and one of them, Rep. Carroll A. Campbell Jr. of South Carolina, said that "we got the impression that he was interested in Vander Jagt."

Another who attended the meeting, Rep. John H. Rousselot of California, said he thought Kemp was still very much in the running.

Rumsfeld also has a smattering of support, particularly if Reagan decides he needs to name someone other than Bush who has appeal among party moderates. Rumsfeld left Detroit this morning, but is scheduled to return Wednesday afternoon.

A close supporter of Reagan said late tonight that "the decision was not cut and dried," that it looked good for Bush, but that Reagan had not told anyone about whom he was choosing -- if he had even made a decision.

Bush spent yesterday stumping before Reagan delegate caucuses as a loyal player on the Reagan convention team, doing his political best to make them forget that there has ever been sharp differences between the two men. He won loud and at times enthusiastic applause for his efforts.

"I don't recall a time in history when the party has been more unified and less divided," Bush told an auditorium filled with an ad hoc group known as the Reagan Youth Delegation. The youths gave him a standing and whistling ovation. "This is a tribute to Gov. Reagan for the way he conducted his campaign. . . . I'm going to work my heart out in the fall. It's absolutely essential that we do not sit on your hands."

Of the eight men who had been listed as finalists in Reagan's search for a vice president, only Bush and Kemp had agreed to serve on panels of surrogate speakers who rode the convention circuit yesterday to address the state caucuses in Reagan's behalf. And Bush was clearly determined to make the most of his assignment.

Appearing before Reagan's home-state California delegation, Bush won warm applause for his effort to blur whatever distinctions once existed between Reagan's positions and his own. "Let me say just a few words about the Republican foreign policy and Gov. Reagan's foreign policy," he said at one point. "They're the same, incidentally, totally the same."

Positions that were once the center-piece of Bush's statements in his debates against Reagan were now presented as Reagan's own, with such introductions as "Gov. Reagan believes . . ." And positions on which Bush once strongly disagreed with Reagan, such as Reagan's call for a blockade of Cuba to counter the Soviet invasion of Afghanistan, were never mentioned.

Bush later explained to a reporter: "Your job is to highlight differences.

My job is not to be helpful about such matters. We're trying to emphasize the things we have together."

While Bush and his advisers were doing no overt lobbying for the vice presidency, the Kemp forces were trying to make the most of their narrower range of support. Kemp aides released a very selective poll of some delegates -- they were the ones mostly favoring Kemp -- and ignoring major Bush states.

Virginia's delegation announced a late-starting petition drive to convince Reagan that Kemp should be his running mate. "We believe he is the most acceptable to the broad base of the Republican Party," said Virginia delegate Guy O. Farley Jr.

It was a day in which all seemed politically forgiven. Reaganites had hit Bush hard throughout the campaign for his membership in the Trilateral Commission and the Council on Foreign Relations, two organizations for the study of international issues that the Reaganites depicted as instruments of global conspiracy.

But yesterday, Reagan's California caucus gave Bush prolonged applause when he answered a question about the organizations with what had become his standard campaign defense, ending with, ". . . To suggest that it's conspiratorial, or that people who belong to it are less than true Americans, I don't go along with it."

Even before Bush appeared before the 168-member California delegation, some conservatives were beginning to see the political merits of his being on the ticket. After Bush's appearance, there were some near-endorsements by conservatives.

Former California lieutenant governor Ed Reinecke, an obscure congressman who hardly knew Reagan when the then-governor picked him as his No. 2 man, said of the California delegation's move toward Bush: "It's a heart vs. head situation. The heart would be with the more conservative philosophy, and that would be Kemp. The head is more pragmatic: who would strengthen the ticket? And that would appear to be Bush."

When Reagan's wife, Nancy, arrived at the California caucus, she had warm smiles and handshakes and whispered kind words for all of the participants, including Bush, whom she is widely reported to oppose for vice president.

Bush enthusiastically applauded her and smiled her way at every appropriate opportunity. He even forced a smile when she told the caucus that "I don't know who the veep is" but that at dinner with the Reagan children and grandchild, "we decided the criteria [should be] who can eat the most jelly beans."

But it was obvious that Bush and his advisers found little genuine amusement in what has become strictly a waiting game. Bush's schedule had been designed with flexibility to allow him to slip away to a meeting with Reagan if the convention's nominee telephoned to summon him. But by nightfall there had been no call.

"I don't like this waiting -- it's nerve-wracking," Bush said late in the day. And of the persistent rumors sweeping the convention that have variously had his chances up and down, Bush said, breaking into to grin:

"They're giving me a tightening peristaltic contraction in my lower colon. We'll have some X-rays soon, in keeping with my policy of full disclosure."