Ted Kennedy did not endorse Jimmy Carter tonight. But he did something much more important for the president and the Democratic Party.

In a powerful speech that electrified Carter and Kennedy delegates alike, he transformed the spirit of this convention, lifted its sullen mood and remined the party's factions that they can cheer and laugh together at the Republicans' expense.

In five striking paragraphs early in the half-hour speech, he recaptured Franklin Delano Roosevelt from the embrace of Ronald Reagan and told the national television audience that quoting New Deal rhetoric was a "trick" the Republicans had unsuccessfully tried to use previously.

Sen. Kennedy showed the Democrats how to isolate Reagan from the Democratic constituencies the Republican nominee has been trying to capture. Kennedy did it by quoting Reagan against Reagan to prove that the Californian is "no friend of labor . . . of great urban centers . . . of the senior citizen . . . of the environment."

And he brought delegates to their feet shouting when he indignantly recalled that the Republican nominee had once linked the New Deal with fascism. "That nominee," Kennedy declared, "whose name is Ronald Reagan, has no right to quote Franklin Delano Roosevelt."

Kennedy's stirring performance prompted a chanting, roaring arm-waving demonstration that went on for more than 30 minutes as the delegates ignored appeals of the normally formidable convention chairman, House Speaker Thomas P. (Tip) O'Neill Jr., for a return to order.

If Kennedy's speech was a boon to the party and to Carter, who will be nominated for president here Wednesday night, the great moment also got people talking about a new political future for the man Carter whipped this year.

In the New Jersey delegation, Carter delegate John Sudia, Democratic chairman in the town of Carteret, said Kennedy's address was "the greatest unification speech" he had ever heard.

"Teddy Kennedy is my man for 1984," Sudia said.

Other New Jersey delegates with Carter buttons on their vests nodded in agreement.

Among Californians, state Assemblyman Willie Brown of San Francisco, a Kennedy delegate, called the speech "a great acceptance speech -- I'm sure it's the one he wrote for accepting the presidential nomination."

In the bitterly divided California delegation, Kennedy's speech struck a responsive chord among the 139 Carter delegates -- many of whom had been openly scornful of the Massachusetts senator the day before.

State Assemblyman Mike Roos, a leader of the Carter forces, was in tears when the speech ended.

"I've never seen so many supposedly sophiscated people moved emotionally by a speech," Ross said.

State Treasurer Jesse Unruh, chairman of the Carter California delegation, agreed.

"It looks to me like Teddy was assigning himself the attack road against Reagan," said Unruh. "Carter can take the high road."

The anti-Reagan rhetoric in Kennedy's speech was rich and plentiful.By contrast, there was a single line on the subject of Jimmy Carter -- a word of congratulations. Kennedy tonight was neither pro-Carter nor anti-Carter. oThe challenger ignored the president and dwelt on the liberal themes he had relied on throughout his nine-month campaign against Carter.

Thus it was not clear whether Kennedy's speech would move the Kennedy backers here to work for Carter in the fall.

Geraldine Wales, a Kennedy delegate from Ardsley, Pa., who said she worked feverishly for "that S.O.B. Carter" in 1976, was sobbing uncontrollably in the final moments of Kennedy's speech, when the senator presented a moving memoir of his travels during the campaign months and the people he met then.

Twenty-seven minutes later, as the band rocked and the "We Want Ted" chanting roared on, Wales was up on her chair, boogeying and waving her blue "Kennedy '80" poster. "I feel rotten," she said. "I'm trying to get up my enthusiasm so I can work for Carter this fall . . . it's not quite working"

The Kennedy delegates were ripe and restless for a major demonstration when Kennedy arrived on the podium just after 8 o'clock. But Kennedy floor managers quieted their partisans, and the senator cut short the cheering by beginning his remarks above the crowd's noise.

The mood in the hall was mellow and restrained during the opening minutes of the speech, but the electricity grew as Kennedy moved into his attack on Reagan. From the moment Kennedy made his "no right to quote" declaration, the excitement and sheer passion of the moment swept like fire through the delegations.

When Kennedy concluded -- "the work goes on, the cause endures, the hope still lives, and the dream shall never die" -- the 20,000 delegates and guests erupted. The cheering reached a pinnacle when Joan Kennedy, who was seated on the podium during her husband's speech, came up and planted a kiss on his cheek.

The couple and their three children then left the platform, but the cheering did not relent. Fifteen minutes later, Ted and Joan Kennedy came back for a final wave, and that ignited new heights of noise and fervor. The delegates shouted, laughed and danced to rock and folk tunes until O'Neill, on his third try, finally got some people to pay attention to the business at hand -- voice votes on the platform.

The reaction afterward was unanimous.

"It was the most beautiful speech I've ever heard," said Kennedy delegate Gus Gentile, 62, of Maryland. "If anything can win the election for Carter and the Democrats, this speech was it.'

Gentile said he had been a Democrat for 47 years, and went door-to-door for Franklin Roosevelt's first campaign.

"He just talked about the traditions of the Democratic Party had what the Democrats stood for, all the things Jimmy Carter has not been able to express," Gentile said.

"Carter has never been able to express himself that way, to do things that appeal to the hearts of Democrats."

Kennedy delegate Mike McGrath of Helena, Mont., said "That was the best speech I've ever heard. It spoke to the concerns and problems of the country. It showed there is hope."

Both men said they would support Carter in the fall, but without enthusiasm.

"It was the greatest thing in the world," said Helen Rogan, a Kennedy delegate from Pittsburgh. "I hope I can get a copy somewhere so I can save it. Such eloquence. Carter could never do that."

Kennedy has made it clear in recent weeks that his long string of losses this year has not soured him on politics; he says he will remain "very active in public life." But he has said nothing publicly -- or privately, according to his aides -- about another presidential race four years from now.

Friends say Kennedy does not think that far ahead. "In my family," he said in an interview this spring, "we have learned that you really can't plan for the very distant future."

Tonight's speech suggests that whatever Kennedy's political future, he will take with him the liberal economics and the firm faith in government that he expressed during his campaign this year. He will also take with him the residual affection of Democrats.

Speechwriters Robert Shrum and Carey Parker, working under Kennedy's close direction, reformulated some of the language, but the substance was right out of the standard 1980 Kennedy stump speech.

Tax reform, increased federal aid to the poor, "jobs for all who are out of work," government help to "reindustrialize" American manufacturing, phasing out nuclear power plants and Kennedy's favorite issue -- comprehensive national health insurance for all -- were in tonight's speech, and most drew a warm reception.

The loudest cheers in this part of the speech came when Kennedy noted that elected federal officials have given themselves federally funded health care. "If health insurance is good enough for the president, the vice president and the Congress," Kennedy said, "then it is good enough for all of you and for every family in America."

It was that line that provoked the widest cheering 30 months ago when Kennedy electrified the party's 1978 midterm convention in Memphis -- and launched his challenge to the president that ended Monday night.

But in stark testament to Kennedy's failed campaign, the delegates earlier today rejected a Kennedy-sponsored platform plank calling for comprehensive health insurance immediately.