United Auto Workers President Douglas M. Fraser, the leading labor supporter of Sen. Edward M. Kennedy, says it is time for dissident Democrats to accept the inevitability of President Carter's renomination and begin reshaping party politics to counter Ronald Reagan's appeal to angry blue-collar workers.

In an interview at his union headquarters this week, Fraser spoke as a man prepared to play a major role in an effort to reunite divided Democrats for the fall campaign.

That effort, he said, will take self-discipline on Kennedy's part, understanding from the Carter forces and a party platform that rejects what Fraser describes as "the harsh, cruel and inhuman" administration policy of "wringing inflation out of the economy by a lot of human suffering."

But the first step, said the leader of the 1.8-million-member union, is to recognize the inevitablility of Carter's nomination.

Fraser gave his personal endorsement to Kennedy on the eve of the Iowa caucuses last January, when the Massachusetts senator was already faltering badly in his challenge to the president. "I said to my people then that there's no point endorsing someone who doesn't need your help," Fraser remarked.

Since then, the UAW has provided key support for Kennedy in most of the major states, and is still working for him in the June 3 primaries in California, Ohio and New Jersey.

But in the interview, Fraser said it is "obvious" that Carter will arrive at Madison Square Garden in August with "300 to 350 more votes" than he needs for nomination. He said it is "ridiculous" to think Carter could be stopped.

"Unless some kind of absolute disaster happens between now and August," Fraser said, "Carter is going to be the nominee." He said that the chances of persuading Carter to step aside for someone else, as New York Gov. Hugh Carey and a few other Democrats have suggested, are "so unlikely . . . I have told them I'm not going to get involved in anything like that."

For the Democrats to emerge from the convention with a chance of defeating probable Republican nominee Ronald Reagan, Fraser said, will require several things.

The first is a willingness by Kennedy to halt his opposition to Carter short of a threat to bolt.

"I don't know how Ted feels," Fraser said, "but it seems to me he will not be interested in engaging in self-destruction . . . or in going so far in terms of his behavior at the convention that even some of his supporters would view it as handing this election to Reagan. . . .

"If he goes over that line," Fraser said, "people will take a very negative view of his political behavior, and start asking, 'Is he really interested in the country, the party, the platform and the principle, or is he only interested in promoting his own candidacy?'"

The second step, Fraser said, must be a mandate from the convention to Carter to change economic policies, which Fraser said have pushed unemployment among his union members to 310,000 this week -- 34,000 more than were out of work in December 1974, the worst month of the last recession.

Fraser said he had noted statements from Carter campaign officials saying they were "open to compromise" on platform planks, if it would help bring such Kennedy supporters as himself back to camp.

He said preliminary talks have begun with leaders of some pro-Carter unions, including Terry Herndon of the National Education Association and William Wynn of the United Food and Clerical Workers, about economic planks their Carter delegates would support.

While Fraser said no decisions have been made, it is clear that he is seeking to build a convention majority for planks that would call on Carter to abandon some of his conservative economic policies -- including the balanced-budget drive -- and swing to the left.

Fraser said, "I question the whole concept of the balanced budget at this time -- and I think a lot of others who will be at that convention, including a lot of the Carter supporters, question it, too. It's not an economic measure, it's a psychological measure, but it is harsh, cruel and inhuman in its effect on our members."

To give force to the platform, Fraser said, he is pushing a suggestion that the convention create a "monitor board" of respected party leaders "to see that a Democratic administration abides by the decisions of the Democratic platform and sort of blow the whistle on them if they don't."

Without such a commitment, he said, the anger and disillusionment of his members -- and their readiness to consider Reagan -- will continue.

"Carter is in deep, deep, deep trouble" with union families, Fraser said, because they think he has broken his economic promises.

As an example, he cited these words from a Carter speech to the 1977 UAW convention: "I am unalterably opposed to fighting inflation by keeping unemployment high and factories idle. This has been done too much in the past. That approach has been proved in the last eight years to be enormously ineffective and morally bankrupt."

Carter then said, Fraser noted: "If the economy should flater during the years ahead, I will not hesitate to propose the economic and budgetary measures needed to get the economy going again, and you can depend on that."

While Fraser sees formidable obstacles to uniting the Democrats, he said that in one respect the problem is easier than it might have been.

"I always held the view," he said, "even way back when it looked like it would be a very close fight" between Carter and Kennedy " that, in terms of putting the party back together it would be easier if Carter won . . . The Kennedy supporters are more committed to the party than the Carter supporters . . . A lot of the Carter people have no commitment to the Democratic Party and its philosophy; they're interested only in electing a president, not in fighting for a program or a platform.

"I told a friend of mine who said this platform thing might be a real battle, 'don't be surprised if this is one of the easier things we ever did. Those people don't care what happens" in the convention "as long as they get their man nominated.'"