Former president Jimmy Carter added a new wrinkle to the nuclear freeze debate yesterday, urging a freeze on all intercontinental strategic missiles -- but not on shorter range missiles based in Europe, where he said the Soviets now have a decided edge.

Carter also said that Defense Secretary Caspar W. Weinberger's latest plan for basing the new MX intercontinental missile, known as "Dense Pack" sounds "ridiculous." The theory behind "Dense Pack" is that if the MX missiles are based close enough together, the blast and radiation from the first Soviet missile will destroy the ones behind it or throw them off target and allow the U.S. missiles to survive.

Because deployment of the MX under this basing plan is "doubtful," a mutual, verified freeze on intercontinental missiles "might be advisable," said Carter, who as president had approved a different MX basing system.

The former president came to Washington yesterday to promote the sale of his book of presidential memoirs, "Keeping Faith," and in the process passed out some free advice and criticism for some current local politicians.

In two sessions with reporters, Carter:

* Urged President Reagan to be "forceful" with Israeli Prime Minister Menachem Begin, when Begin arrives in Washington for talks on Nov. 19. Carter said he doesn't believe Begin is committed to "the principles, and the spirit, and the letter of the Camp David agreement," which was perhaps the finest hour of his presidency.

* Criticized Walter F. Mondale, who served as his vice president, for having made "extremely vituperative attacks" on the Japanese trade policies in recent speeches. He called Mondale's public expressions "confrontational," "troubling," and "counterproductive"--a "wave of protectionism" he said Mondale was riding to win labor union support. He also said that Mondale still remains his first choice for the 1984 Democratic presidential nomination.

* Declared that Sen. Edward M. Kennedy's presidential ambitions remain hampered by "obstacles," even though the Massachusetts Democrat is the frontrunner for the party's 1984 nomination according to all polls. But Carter recalled that his own polls in his bitter battle with Kennedy for the 1980 presidential nomination showed that there was a "sharp distinction" in the nature of Kennedy's support.

People were telling pollsters they favored Kennedy because they found him an "exciting candidate," Carter said, but when pressed by his poll-takers as to whether they really wanted Kennedy to be sitting in the Oval Office, Kennedy's support dropped sharply. Carter said he did not know whether Kennedy could ever overcome the "obstacles."

Carter amplified yesterday on the brief disclosure in his book that he had proposed a freeze on nuclear weapons in his Vienna summit meeting with Soviet President Leonid Brezhnev.

Brezhnev and the other Soviet leaders rejected the U.S. freeze proposal, Carter said yesterday. But it was unclear how vigorously Carter had pressed the freeze proposal or whether he followed up on it.

In his book, Carter says that he and his advisers in Vienna "decided that a total freeze in production and deployment of all nuclear weapons would be advantageous if it could be implemented without delay and if adequate verification procedures were devised."

Yesterday, Carter said that he made this proposal both at the negotiating table in Vienna and in a private conversation with Brezhnev, where only Brezhnev's interpreter was present. He said the Soviet leader rejected the freeze proposal both times.

"The reason he did, we now know -- and suspected then -- was so they could complete their deployment of the very formidable SS20s," he said, refering to the powerful intermediate range missiles deployed in the European theatre by the Soviets.

Carter said the Soviets have continued deploying the SS20s at a rate of one a week and because of them the Soviets have a significant "advantage" over NATO forces in Europe. Thus, he opposes a freeze that would include them but he does favor freezing longer range intercontinental missiles.

"There is a rough equivalency -- an adequate equivalency -- in intercontinental missile capabilities," Carter said.

He didn't explain why, with "adequate equivalency," he believed the MX missile was needed during his presidency. Carter approved a "shell game" concept of basing the MX missile, in which there would be a number of different silos for each missile with the missiles shuttled around them, making it difficult for the Soviets to target them.

In the Democratic presidential race, Carter said that while Mondale remains his first choice, he is not going to campaign for anyone.

"Obviously, Fritz, in his political wisdom, wants to separate himself from me," Carter said. "There is a lot of baggage that goes with me and my administration."