Walter F. Mondale today unloaded a withering critique of his debate opponent, calling the President Reagan of the Kansas City debate a dangerously "detached, remote and misinformed" leader who tried to shuck responsibility for his foreign policy failures.

"Last night, the American people saw with their own eyes what the problem is," Mondale told a lunch-hour rally of 15,000 at JFK Plaza here. "They saw a president who cannot discuss any major issue without making a major mistake . . . . They saw a commander-in-chief who is not commanding and who isn't a chief."

With his slashing reviews, Mondale was bidding gamely to "win" the replays of a debate that most observers, media commentary and overnight polls had judged a draw.

Mondale's strategists conceded today that they will get no immediate momentum shift from the televised foreign-policy exchange, but campaign chairman James A. Johnson vowed that "last night's debate won't be over until Nov. 6."

He said Reagan's statements and misstatements had provided ammunition for Mondale to focus the final two weeks of the campaign on questions of war and peace and on presidential competence.

Today's attacks suggested how differently the Mondale camp viewed this debate from the first one. After Louisville, Mondale had the liberty of letting the media carry the criticism of Reagan's shaky performance. Today, it was Mondale's turn.

Mondale warmed to the task with ridicule and indignation, and he attacked from the left and the right. On the Reagan proposal to share advanced-weapons technology with the Soviet Union, Mondale said, "That's not my idea of strength."

"We climbed the rock of strength last night," said Mondale's foreign-policy adviser, David L. Aaron. "Now we can really focus on the nuclear issues."

Mondale said today that Reagan was flatly wrong Sunday night when he denied that he had ever said submarine-launched missiles could be recalled. "We cannot permit and we will not tolerate a president who does not know what he needs to know," he said.

He accused Reagan of trying to escape responsiblity for the barracks bombing that killed 241 U.S. servicemen in Beirut last year. "He said, 'I didn't do it. It was a local commander who made a mistake.' That's not what we expect of a president," Mondale told a group later today at Bergen Community College in Paramus, N.J.

On a related issue, aides to Reagan denied Mondale's assertion Sunday night that the Joint Chiefs of Staff had advised that Marines be withdrawn from Lebanon shortly before the barracks bombing. "It's absolutely false," said Robert C. McFarlane, Reagan's national security adviser.

On the controversial CIA manual in Nicaragua, Mondale said: "Mr. President, that's your secret manual. You bought it and paid for it. It's your secret war. Those are your terrorists. And it's your quagmire that we're headed for in that nation."

He ridiculed the president's proposal to give the Soviets a demonstration of space weapons, likening it to calling "the Soviets in for a little nuclear skeet shoot."

At Bergen Community College, he added: "Mr. President, over what state are you planning to do that demonstration shot?" The question drew widespread laughter.

Mondale's crowds today were not as effusive as those that greeted him after the Louisville debate. At the Bergen Community College, there were some scattered Reagan chants.

Today's swing to Pennsylvania, New Jersey and New York marked the beginning of a 15-day finishing dash for Mondale. He will barnstorm through the Northeast and Midwest this week, and on the weekend he will take his fourth post-convention trip to California, with a brief stop in Texas.

Campaign manager Robert G. Beckel said Mondale is now running ahead in the Northeast industrial states -- a statement that Reagan strategists called "whistling past the graveyard" -- and is "very competitive" in the Midwest and on the West Coast. "The race in California is going to be very close," he said, "down to the margin of turnout."

Beckel gave no poll numbers to back his claims. He did say, however, that a poll of 650 voters taken after the debate by the Mondale pollster, Peter Hart, showed Mondale had won the showdown, 35 to 30 percent.