Sen. Edward M. Kennedy ripped into Ronald Reagan tonight and transformed a dispirited Democratic National Convention into a cheering mass with a prediction that the Democratic Party will reunite and "march toward a Democratic victory in 1980."

In an emotional appearance before a convention he once hoped would give him the presidential nomination, Kennedy stopped short of an explicit personal endorsement of President Carter and made clear his continuing differences with Carter's economic policies.

But he also provided the convention with an electric moment of unity that the president needs so badly, as his delegates and those pledged to Carter stood together cheering his denunciation of Republican nominee Reagan.

And when the speech was over, the convention, at least for the moment, belonged to Kennedy, even if the nomination is Carter's. His cheering, stomping supporters, shouting "we want "Ted," demanded that he return to the podium.

Kennedy, with his wife, Joan, beaming at his side, reappeared on the podium, setting off renewed cheering. In all, the demonstration for him lasted more than 40 minutes. While it continued, the Carter camp hastily decided to capitulate on most of the economic issues that originally brought Kennedy to the convention hall to plead his case.

Kennedy's only mention of Carter at the end of an address that was clearly once designed to be his own acceptance speech, did not contain an outright pledge to support the president in the fall campaign.

"I congratulate President Carter on his victory here," Kennedy said. "I am confident that the Democratic Party will reunite on the basis of Democratic principles and that together we will march toward a Democratic victory in 1980."

But except for the implied criticism of the president's economic policies as a turning back from Democratic traditions, the tone of the speech was not anti-Carter, and the sharp attack on Reagan was just the medicine the convention seemed to need.

"If he goes on making fine speeches like that, he could be a lot of help to President Carter," White House press secretary Jody Powell said as the demonstration continued on the floor of Madison Square Garden and the delegates broke into song.

Even before Kennedy arrived in Madison Square Garden, it was clear that the Carter campaign was in trouble on the economic disputes.

The debate that preceded the senator's appearance took place in a noisy, emotional atmosphere. Carter's name was booed several times by delegates waving Kennedy signs and blue Kennedy balloons. Attempts by pro-Carter speakers to promote a compromise on the jobs dispute produced sustained booing and a response from pro-Kennedy speakers that "there is no compromise when it comes to jobs for Americans."

After Kennedy raised the emotion level of the highest of the convention, the president's strategists had had enough.

They dropped a plan for a roll-call vote on one minority report supported by Kennedy and left the outcome of the economic disputes to voice votes on which convention chair man Thomas P. (Tip) O'Neil Jr. could rule as the Carter forces wished.

O'Neill ruled that a minority report calling for mandatory wage and price controls, which Carter adamantly opposes, had been defeated, setting off a chorus of boos. But on three other minority reports, including one that calls for a $12 billion economic stimulus program that was to have been the subject of the roll call, the House speaker called it for Kennedy.

Thus the convention approved planks that were originally drawn up by Kennedy supporters in June as implicit repudiations of some Carter administration economic policies.

Specifically, the planks insist that the Democrats will not adopt policies that deliberately raise interest rates or cause unemployment as tools to fight inflation.

Capitulation to the Kennedy camp on these points was not the only setback for the Carter administration here today. Earlier, the full convention amended the platform to require Democratic candidates to support the Equal Rights Amendment or lose all party aid, and to support the use of federal funds for poor women's abortions. Both votes pleased feminist activists here, and both went further than the White House wanted to go.

The full convention also adopted a key Kennedy economic proposal on a roll-call vote. It altered the platform to say that creating jobs is the Democrats' first priority, even more important than fighting inflation.

Throughout the convention hall tonight, the reaction to Kennedy's speech was favorable.

"That was an excellent speech," Lillian Carter, the president's mother, said. "I don't see how he could have lost with that speech."

Detroit Mayor Coleman Young, a strong Carter supporter, called it "a very good speech, the best I've heard so far in the convention."

In the hours leading up to the debate over the economic report, it was clear that tonight would be Kennedy's moment at the convention.

When the Massachusetts senator reached the podium as the last speaker of the debate, the emotions of his supporters, which had been building during the earlier speeches, exploded.

The convention floor became a sea of blue-and-white Kennedy campaign signs as the delegates cheered and the band played "McNamara's Band."

Saying he came to the convention hall "not to argue for a candidacy but to confirm a cause," Kennedy appealed to the delegates "not to forsake" the tradition of the Democratic Party.

"We cannot let the great purposes of the Democratic Party become the bygone passages of history," he said."We must not permit the Republicans to seize and run on the slogans of prosperity."

Kennedy then turned his fire on Reagan and the Republicans, and as he did, the Carter supporters, who had been largely silent but polite, joined their Kennedy counterparts in the cheering.

"The great adventure which our opponents offer is a voyage into the past," he said. "Progrress is our heritage, not theirs. What is right for us as Democrats is also the right way for Democrats to win."

Kennedy's criticism of the president was implicit and indirect as he called on the convention to pledge "that we will never misuse unemployment, high interest rates and human misery as false weapons against inflation."

But in giving in to Kennedy on most of the economic disputes that were the cause of tonight's debate, the Carter campaign made yet another move toward turning the senator into a full-fledged partner of the president by the end of this convention Thursday night.

With the demonstrations for Kennedy still going on, Carter campaign chairman Robert S. Strauss told reporters of the agreement to have O'Neill rule for Kennedy on all but wage and price controls.

"This is a unity reception," Strauss said. He called Kennedy's speech "very good -- yes, certainly it was an endorsement. I don't know how else you could attribute it. It will be an asset to the fall campaign."

As the convention began debating the platform, the Kennedy forces won a preliminary skirmish when the delegates adopted, by an almost 400-vote margin, a minority report declaring that the guarantee of a job is the party's "single highest domestic priority."

Feminists at the convention also won adoption of two planks, one that would deny party financial aid and other assistance to any candidate who does not support the Equal Rights Amendment, and another favoring the use of Medicaid funds to pay for poor women's abortions.

But the main focus of attention was on Kennedy's appearance at the convention tonight and the debate over his call for a $12 billion economic stimulus package to create jobs.

Talk of compromise on this issue, which arose in the aftermath of Kennedy's withdrawal from the race, quickly evaporated as the senator's aides insisted, in the words of one, that "we ought to have a full and open debate visible to all of the people."

Before Kennedy's speech transformed the atmosphere tonight, many of his supporters seemed restless and unhappy, contributing to a sense of gloom about the fall campaign ever among many Carter supporters.

By tonight, some signs being waved in the crowd declared that 1984 would be Kennedy's year. There was no open discussion of that tonight, but nothing in Kennedy's rhetoric or the strength of his delivery suggested he has foreclosed another run for the presidency.

For Carter, however, the key question was whether the enthusiasm generated by his rival will make unification of the Democratic Party easier and translate itself into support for the president this fall.

There was no sign of a widespread revolt by Kennedy delegates, but pockets of bitterness at the end of the long campaign were evident.

Former Wisconsin governor Patrick J. Lucey, Kennedy's deputy campaign director, resigned as a member of the Wisconsin delegation and said he would "reserve the right" to support a candidate other than Carter.

Lucey, once Carter's ambassador to Mexico, said he resigned to protest Monday night's adoption of the rule binding delegates to vote for the candidate they are pledged to, thereby assuring the president's renomination.

Longtime liberal activist Joseph L. Rauh Jr. said he "can't vote for Carter" and suggested that he will support independent candidate John B. Anderson.

The president's strategists said they recognized that the Kennedy delegates were suffering an emotional letdown and that party unity would not be instantly achieved. Hamilton Jordan, the Carter campaign's chief strategist, predicted that "with hard work in the next few days" the bulk of Kennedy's supporters would get behind the president.

But the hoped-for compromise over the main economic issues, a hope that cropped up after Kennedy's unexpected withdrawal Monday night, fizzled in the cold light of day. Telephone conversations between top aides of the rivals this morning soon established that, on those subjects, there was not much to talk about.

"The senator's feeling is that the delegates ought to decide," said Kennedy's issues director, Peter Edelman.

"There are real differences between Sen. Kennedy and the president in this area," said White House press secretary Jody Powell. "That's why we have had a long campaign. These are two strong and determined men and neither should be expected to abandon his principles."

The day's debate on the platform revealed that the delegates who on Monday night signaled an overwhelming desire to renominate President Carter do not necessarily agree with him on all the issues.

This became clear in the symbolic vote on a proposed amendment to the platform that declared that jobs for the unemployed are more important to the Democratic Party than "all other domestic priorities," including the fight against inflation.

This was a Kennedy proposal, one that the Platform Committee rejected overwhelmingly in June. But it was approved today, and by a surprisingly large margin, 1,764 votes to 1,391.

The White House had opposed this change on grounds that inflation ought to be seen as the administration's principal concern. Gov. Jim Hunt of North Carolina, a Carter supporter, made that point explicitly in today's debate in the convention hall.

"Do we really want to say . . . that fighting inflation will take a back seat in the platform of the Democratic Party?" Hunt asked. "Do you want to say that to the young couples in your state who are hoping to buy a home of their own" but are victims of inflation?

Rep. Shirley Chisholm (D-N.Y.) spoke for the proposal, emphasizing that her concern was with poor, unemployed Americans, not young couples trying to buy homes. Invoking all the Democratic presidents since Roosevelt. Chisholm asked if the Democrats had become "a party that would covet victory even at the price of joblessness?"

The answer from the delegates was an overwhelming no.

Activist women also demonstrated political influence greater than the White House's today. At their urging, the convention approved two controversial changes that the Carter camp would have preferred to live without.

One of the proposals stipulates that the party "shall withhold financial support and technical campaign assistance from candidates who do not support the Equal Rights Amendment." Opponents complained that this sort of litmus test discriminates in favor of a single issue -- ERA -- and thus contradicts the struggle for women's equality. But the convention adopted the change by an overwhelming voice vote.

The convention also put the Democrats more clearly on record in support of abortion than the White House had wanted. It approved, 2,005 to 956, an amendment, pushed by the National Organization for Women and other activists, favoring use of Medicaid funds to pay for poor women's abortions.

The amendment does not mention abortions or Medicaid directly. Instead, it opposes government policies that limit the "reproductive choices" of poor women. But the intent is clear.

The convention took Carter's side in a policy dispute with the Kennedy forces over national health insurance. The Kennedy camp had proposed an amendment committing the party to a comprehensive health insurance bill specifying when the full range of benefits would come into force. The White House prefers a vaguer formulation, without any reference to a timetable. This approach prevailed, 1,573 to 1,349.

Wednesday the convention will continue debate on the platform. The most controversial issue is likely to be the MX missile. On Wednesday night the convention is scheduled to nominate Carter for a second term.