With victory in the rules fight and renomination apparently assured, President Carter tonight agreed to accept four of Sen. Edward M. Kennedy's platform amendments -- including a pledge not to use unemployment or high interest rates to fight inflation.

The unilateral concession was designed to swing Kennedy and his backers behind the president in the general election campaign, but Kennedy continued to be coy about his plans.

He welcomed the Carter move but said he would fight for other changes in the platform, and he withheld any direct promise to back Carter.

As caucuses continued on the eve of the convention's opening, roving teams of Carter campaign whips hammered home the message that his delegates must reject the Kennedy effort to defeat the convention rule binding delegates to their condidate pledges. The "open" convention forces appeared well short of a majority on the roll call that will come Monday night.

As the uncertainty evaporated from that fight, attention shifted to the chances for reconciliation of Carter and Kennedy and the two factions that have been battling with increasing bitterness for the last months.

Kennedy opened the door to a possible appearance with Carter at the losing convention's Thursday night closing ceremony in an interview on "Face the Nation" (CBS, WDVM). He said that when he is convinced that Carter had accepted some of his economic policy recommendations "as a matter of substance . . . and not just cosmetic commitment, there won't be any Democrat in this country that will work harder for the success of the nominee" than Kennedy.

In announcing the Carter platform concessions a few hours later, the president's chief domestic adviser, Stuart Eizenstat, adopted Kennedy's language. Speaking, of the decision announced today, Eizenstat said, "They are not cosmetic. The president takes this platform seriously."

Eizenstat said the concessions were not a direct response to Kennedy's apparent overture on television, but had been authroized by Carter several days ago.

Nonetheless, they swung the momentum in the convention city away from confrontation and toward the possibility of reconciliation. Carter aides were obviously relieved at the improving prospects for avoiding a bloodbath and perhaps enlisting Kennedy's help as well.

"Obviously, a Democratic victory in November would be easier with the support of Sen. Kennedy and all the Democrats," White House press secretary Jody Powell said.

Kennedy was not ready tonight to make that kind of commitment. Telling reporters that the planks Carter had agreed not to fight would have been "accepted overwhelmingly by the delegates" in a floor fight, he said, "There are a number of other economic issues we'll continue to debate."

The concessions Eizenstat announced included one plank on which Kennedy had focused -- a pledge that "the Democratic Party will not pursue a policy of high interest rates and unemployment as the means to fight inflation."

The Carter forces were saying tonight that they would still fight another key Kennedy platform amendment, a proposal for a $12 billion antirecession public employment program.

Kennedy is scheduled to debate that plank on Tuesday night, but Gary, Ind., Mayor Richard G. Hatcher and other black leaders were working for a compromise that could sidestep the issue without a showdown vote.

Hatcher, a Carter supporter, said he and other mayors could accept a program half the size Kennedy is proposing, but might swing behind the senator if the Carter forces remained adamant. Some Carter aides were talking compromise, but the president's readiness to yield further to Kennedy appeared contingent on a further indication of a conciliatory mood from the senator.

For the moment, the Kennedy forces were enjoying what Paul Kirk, a top Kennedy aide, called "the first real victory" of the convention.

Kennedy said Carter had bought his position "lock, stock and barrel," and said, "This is getting to be the kind of platform that I welcome to run on and take across the country."

There was no evidence that he would have the chance. As delegations caucused on the "loyalty rule," the Carter forces appeared to be matching or exceeding their predicted strength on the issue. In California, for example, a worrisome "soft spot" for several days to the Carterites, all 139 Carter delegates voted for a resolution backing the president on the rule. In Ohio, where there were reports of "softness" last week, Carter delegates were unanimous in their continued support of the president. In Michigan, two delegates who went public last week with their intention to consider breaking with the president were firmly back in the fold.

Meantime, midtown Manhattan was transformed from the torpor of an August Sunday afternoon into the kind of urban jamboree that only a Democratic convention seems to produce.

The lobby of the plush Waldorf-Astoria Hotel was occupied by a group from ACORN, a low-income people's action group. Traffic outside the Statler hotel, the convention headquarters, was stymied by demonstrators, gawkers and mounted police.

Almost everyone had a cause -- an "open" convention, equal rights, gay liberation. Members of the different groups seemed to accept each other's activities as a welcome relief from the summer doldrums.

The scene on the streets had its counterpart in the headquarters of the Democratic National Committee and the Carter campaign, where officials talked more optimistically than they had in weeks about the chances of avoiding a series of bitter floor fights that could endanger Democratic prospects in November.

Even before the Carter platform concessions were announced, Kennedy had began to alter his tone of unremitting opposition to the president on every major issue before the convention.

For the first time since making the "open" convention issue the corner-stone of his last-ditch drive to deny Carter renomination, the senator said that loss on that issue would not in itself cause him to refuse Carter support in the general election comapaign.

Asked if Carter's refusal to "release his delegates would, by itself, be an insuperable barrier to your supporting him as the nominee," Kennedy answered with an unqualified "no."

That told the Carter forces that beating him on Monday night -- as they expect to -- would not mean automatically losing him from the podium in the unity pageant they hope to stage Thursday night.

Instead of pegging his future cooperation to the rules issue, Kennedy said the price of his backing Carter would be the party's clear rejection of "the economic concepts of high-interest rates and high rates of unemployment as solutions to the problems of inflation."

"I'm prepared to see this party unified, to see this party successful," Kennedy said. "I believe that it is important for the country."

He said that the election of Republican nominee Ronald Reagan would be bad for America, "because I think Mr. Reagan has rather simplistic solutions to the major problems that we're facing today."

Later, Kennedy told the California delegation that "californians know the nature of the opposition in Ronald Reagan -- and know how bad things can really be." He told another group on his day-long swing through the caucuses, "The things that unite us are more important than the things that divide us."

But Kennedy made it clear that he was not calling off his fight to break the "loyalty rule" Monday night and would be pressing the rest of his economic package personally in Tuesday evening's platform debate.

Warning against what he called "cosmetic commitments" on Carter's part, Kennedy said that if he was still skeptical of the economic direction the president intended to take, "then I [would] have real difficulty in indicating to the millions of Americans who have supported my candidacy" that they should work for Carter.

Eizenstat did his best to depict the Carter platform concessions as substantive, even while insisting they had not been dictated by Kennedy.

In addition to the main plank eschewing high-interest rates and unemployment as cures for inflation, the Carter forces accepted Kennedy provisions promising:

Not to cut social programs for the sake of balancing the budget and exercising fiscal restraint alone.

Opposition to "special-interest efforts to undermine" federal regulatory efforts.

To boost federal support for solar and other unconventional renewable energy sources, rather than pushing synthetic fuels or nuclear power development.

In addition, Eizenstat confirmed that the Carter forces would no longer oppose a Kennedy-suggested rule requiring potential nominees to state their positions on the platform in writing before the convention balloting takes place.

That provision, Eizenstat noted, would allow Carter to certify his general agreement with the platform and to specify areas where his own campaign position may diverge from the platform.

The concession today by Carter reduced the number of platform battles coming to the convention floor from the original 18 to nine.

Some of them appeared to be a retreat by Carter from the past policies of his administration that Kennedy has been criticizing in his campaign. But Eizenstat said the president felt he could yield because his own anti-inflation policies were designed to minimize unemployment and create jobs. a

As for the budget language, Eizenstat said, "While we had to make some very large budget cuts to pierce inflationary psychology, we made every effort to protect vital social programs."

As the hopes for a harmonious end to the Madison Square Garden convention increased in the Carter camp, the president's aides did all they could to make it easy for the senator to endorse the incumbent. A long afternoon meeting between Kennedy assistants and aides to Carter and Vice President Mondale ended with one of the Carter men saying the president was "ready to move at a moment's notice" if Kennedy's Tuesday speech signals the challenger's readiness to make peace.

While Carter stayed in touch with developments from Camp David, Md., Mondale expressed the hope that Kennedy "will find it possible to support the ticket."

"I know Sen. Kennedy is well aware of Mr. Reagan and his policies and of the disastrous consequences they would have. They would undermine and destroy everything we have fought for," Mondale said.

Carter campaign chairman Robert S. Strauss, who was sharply critical of Kennedy's anti-Carter rhetoric as recently as Friday, said he welcomed the change in the senator's tone. "We want his support," Strauss said.

But, still nervous about how Kennedy would decide to play his convention hand, both Strauss and Democratic National Committee Chairman John C. White denied that the senator's endorsement was vital to Carter's prospect for success on Nov. 4.

Straus said "90 percent of Kennedy's supporters" would rally behind Carter no matter what Kennedy did. White said that "when it really comes down to voting. I don't think it makes that much difference" what Kennedy does.

Privately, however, leading Carter strategists made it plain that they not only want Kennedy's support but also hope that agreement comes early in convention week, before television viewers are treated to hours of anti-Carter rehetoric from the Kennedy delegates.

A Washington Post poll in late July said that only four in 10 of the Kennedy delegates were going to New York mentally prepared to support Carter enthusiastically if he won the nomination. The rest said they would back him only reluctantly or not at all.

The fast-moving developments pointing toward the possibility of a Carter-Kennedy platform reconciliation took some of the emotional edge off the Monday night rules debate. But neither side was easing off a bit in its effort to win that test.

Kennedy said the issure would be decided by margin of 50 votes "one way or the other." But Strauss said he was absolutely certain "we will win it and reasonably certain we will have over 300 votes. That campaign is over."

The debate on the "loyalty rule" is scheduled to begin at 6:30 p.m., with the roll call occurring an hour later. The rule in question would allow a candidate to replace any delegate who threatens to break his or her pledge of support with an alternate of unquestioned loyalty.

The principal speaker in the debate, which will provide the first moment of drama in the convention, will be Sen. Abraham A. Ribicoff (D-Conn.) for the Carter side.

Ribicoff, a longtime friend of the Kennedy family, made the nominating speeches for Sen. George McGovern at the 1968 and 1972 conventions, so there is emotion as well as great political consequence in the exchange.

Both sides agree that the last hope of the stop-Carter forces will disappear if the president's side prevails on the rules issue. Carter has 1,985 delegates, compared to 1,243 for Kennedy with 103 uncommitted, according to the United Press International scorecard.

The Carter forces announced that other speakers in the debate will include mayors Maynard Jackson of Atlanta, Dianne Feinstein of San Francisco and Hatcher of Gary, Ind., Gov. Ella Grasso of Connecticut and South Carolina Democratic chairman donald Fowler.

It was uncertain tonight whether the "open" convention advocates who are not backing Kennedy would have a voice in the debate. The uncommitted group, whose organizers are interested in seeing Mondale, Secretary of State Edmund S. Muskie or Sen. Henry M. Jackson (D-Wash.) nominated, was planning to go to the rules committee Monday in an effort to secure time for its spokesmen.

The Committee to Continue the Open Convention also ran into trouble in getting state delegations to hear its presentation. It was turned down by Iowa, Oklahoma, Maryland and the National Education Association caucus, the Associated Press reported.

Meantime, several of the people Kennedy had listed Saturday as possible running mates issued statements today declining the honor. Former Florida governor Reubin Askew, Sen. Adlai Stevenson of Illinois, Rep.Lindy Boggs of Louisiana and Los Angeles Mayor Tom Bradley all said Kennedy had failed to consult them before throwing their names into the convention speculation.

Jackson, who had been contacted by Kennedy, said he was flattered but "I'm not running for vice president."