The last Republican president and the man who wants to be the next one met privately for 90 minutes today and then emerged for a joint denunciation of President Carter.

In an informal news conference with reporters alongside the 13th hole of a sunswept golf course outside his office, former president Gerald R. Ford said that Ronald Reagan was now acceptable to him, and predicted that he would defeat Carter in November.

"I feel very strongly we have to make a change in the White House, and I am convinced Gov. Reagan can be elected . . .," Ford said.

Reagan, dressed in a suit and tie on a scorching day in this desert community, let Ford, informally attired in sports clothes, do most of the talking.

And talk Ford did.

He said that Carter's economic policies were a "catastrophe" and a "disaster," and said that the incumbent Democratice president had the worst economic record to defend since Herbert Hoover.

Ford offered to campaign strenuously for Reagan, and the former California governor in turn said that he wanted all of Ford's help he could get.

It has been an open secret that Ford and Reagan have no great fondness for each other. Ford was known to resent Reagan's stiff challenge to him in the 1976 primary campaign and he on occasion termed the Reagan challenge one of the reasons for his defeat in November. In his autobiography, Ford accused Reagan of advocating "simplistic solutions" for complex problems.

Reagan has always seemed reluctant when it came time for praising Ford, although he did campaign for the Ford-Dole ticket in more than 20 states.

Today however, both men expressed apparently genuine regard for each other. Ford said that he thought Reagan had moderated his position on several issues and that he agreed with most of the things Reagan had been saying during the 1980 primary campaign.

"My view of politics has always been to look ahead and not worry about the previous innings of a ball game," Ford said.

Reagan said that some of the misunderstandings of the past were because of a failure of communication at the staff level in 1976. He said he wanted Ford's counsel and planned to have other meetings with him during the campaign.

However, both men said that a date for a subsequent meeting has not been set.

In discussing the upcoming meeting Wenesday, Reagan campaign director William J. Casey said that selection of a vice presidential running-mate was "the most critical choice" for Reagan and indicated that the former governor would discuss vice presidential possibilities with Ford.

Ford is believed to favor defeated Republican candidate George Bush, who was assisted by several former Ford aides, as Reagan's running mate. But Ford said he had not discussed any names with Reagan, though he had told him that he would be available to make recommendations if Reagan wanted him to.

The ultimate decision must be Reagan's, Ford added.

Ford firmly ruled himself out as a vice presidential possibility on the grounds that such a selection would violate the provision of the U.S. Constitution requiring that the president and vice president have different states of residence.

Some advocates of a Reagan-Ford ticket have suggested that the former president could claim his home state of Michigan or Colorado, where he has a residency at Vail as his home Ford said this would be a "gimmick" and a "phony operation" to circumvent the Constitution and that he would have no part of it.

Ford did say that he had praised Henry A. Kissinger to Reagan and recommended a specific assignment for him in the campaign. But he declined to tell reporters the nature of his recommendation.

Ford also was asked whether he thought that the Republicans would benefit this fall from the continuing conflict between President Carter and Sen. Edward M. Kennedy, (D-Mass.) who had their own meeting in the White House today.

Ford predicted that "our Democratic friends" will get together as they have in past campaigns.

"I think you'll see Jimmy Carter and Ted Kennedy put their arms around each other in a love feast . . .," Ford said with a grin.

One of the few questions Reagan answered at any length concerned whether people had a misperception of him.Reagan agreed that many people did.

"There is a basic belief that I am lacking in compassion . . . and that I would balance the budget on the backs of the poor," Reagan said. "My record as governor reveals that none of that is true."

Reagan accompanies only by Casey, attended the meeting with Ford. Near the end of the news conference, Betty Ford came out of the office and joined Reagan and her husband. Nancy Reagan was not present.

Ford seemingly in a happy mood, joked with reporters on the lawn earlier in the day while waiting for Reagan to arrive. He was asked where he thought the summer White House would be at this time next year.

"I think I would gamble on some place in California," Ford said.