Frankly astounded that their own predictions had come true at last, the Kennedy-for-President people took time off from celebrating tonight to chart a future campaign course that will focus on the April 22 Pennsylvania primary.

Although all such decisions seem subject to rapid change, the early line here among Kennedy advisers was that the candidate would not make an intensive personal effort in Wisconsin and Kansas, which will hold primaries next Tuesday.

Instead, Kennedy's thinkers were telling him that the best way to cash in on his big victories tonight in New York and Connecticut would be to channel his time and money first into Pennsylvania and thereafter into other big industrial states.

How long this would remain the guiding wisdom was unclear tonight, because most of the Kennedy campaign people here were too busy trading "I told you sos" with reporters to focus on future strategy.

In a way, they did tell us so. For the last three days, Kennedy and his closest advisers had been saying that they felt movement among New Yorkers away from Carter and toward them.

But they clearly did not feel a movement as sweeping as the victories they scored in both states tonight. Even the candidate, who has shown little reluctance during his campaign to make extremely optimistic predictions, refused to say outright that he would win here.

And the Kennedy people decided not to set up an election night party in which the candidate could greet a room full of campaign volunteers. "We've had those crying volunteer shots on the tube just about every Wednesday morning," a Kennedy aide said, "and we figured, why do it again?" word went out that all volunteers were to gather at a midtown hotel, and there Kennedy told the chanting, cheering crowd that Carter's failure to campaign was his downfall. "No one who has stayed in the White House for six months," Kennedy shouted, "can understand the human needs of the people of New York and this country."

After spending most of the day in Washington, Kennedy flew down here to receive the returns with two dozen friends at the Manhattan home of his brother-in-law and campaign manager, Stephen Smith.

Kennedy arrived at Smith's before the voting booths had closed in New York, but the pollsters were already projecting victory for him in both states.

When he walked into Smith's elegant East Side home, he was greeted with an enormous cheer and a big kiss from his sister, Jean Smith.

In claiming victory tonight, Kennedy was calmer and more serious than he has been on the several nights this year when he has conceded defeat.

Accompanied by his wife, Joan, who said she was so happy she felt like singing, and his two oldest children, Kennedy appeared before a hall full of reporters and read a statement in which he said that the voters "are sending a very clear and powerful message . . . that they can no longer afford an inflation rate of 18 percent and interest rates that match."

Asked if his victories tonight indicate that the "character" issue is no longer a factor, Kennedy suggested that the vote meant that people are more concerned about the country's current problems than about his past. "The message that they sent is that this administrtion has failed," he said.

The candidate allowed himself a moment of gloating at the expense of two New York Democrats, Gov. Hugh L. Carey and Sen. Daniel Patrick Moynihan, who urged Kennedy to enter the race last summer but failed to lift a finger to help him thereafter.

"They gave me very good advice," Kennedy said. "They said I could carry New York and, by God I did."

When things were looking grim for Kennedy here -- that is, just a few days ago -- campaign aides talked wistfully about the prospects in Wisconsin, a liberal state where Kennedy's campaign is being run by a popular former governor, Patrick Lucey.

But Kennedy has been able to afford only a minimal organization in Wisconsin, and in the view of almost all his staff, polls there suggest that he may be too far behind President Carter to catch up, even with the psychological boost he got tonight.

Paul Kirk, Kennedy's chief political strategist, said Wisconsin was not a fruitful target because its primary has been challenged as a violation of the party's rules on delegate selection. Republican John B. Anderson is likely to draw Democratic "crossover" voters who might otherwise support Kennedy, and 'there's not enough time to put together a serious effort there," Kirk said.

"The polls are pretty rough out there," said the candidate's nephew, Robert F. Kennedy Jr., 27. "We might do better to concentrate elsewhere.'

But such predictions are written on water at a time when the campaign is still savoring two victories it had not expected. Kennedy has scheduled two days of rest and planning in Washington Wednesday and Thursday, and thereafter a clearer campaign plan will presumably be developed.