President Carter, asserting that a strategic arms limitation treaty (SALT) can be "adequately verified," said yesterday the Soviet Union knows that cheating could ruin its good relations with the United States and "escalate into a nuclear confrontation."

Defending his administration's move toward a SALT II agreement with Moscow, the president said at a press conference:

"If the only purpose of the Soviet Union in the long, tedious negotiations of a SALT treaty is to have a document that they can violate . . ., it would make our problem much worse.

"But," he added, "there is an element of rationality and stability because the Soviets know that it we ever detect any violation of the SALT agreement, that that would be a basis on which to reject the treaty in its entirety; there would be a possible termination of the good relationships between our country and the Soviet Union on which detente is based, and it might very well escalate into a nuclear confrontation."

Agreement on SALT II is expected within the next few days, and it is expected to be signed shortly afterward at a summit meeting of Carter and Soviet President Leonid 1. Brezhnev.

But the treaty then faces a difficult battle for approval by the Senate. When Carter was asked yesterday about reports that the United States would need from one to four years to be able to fully verify Soviet compliance with its restrictions, the grasped the opportunity to make a new sales pitch for the agreement.

The president conceded that Defense Secretary Harold Brown had said it would take a year to compensate for the loss of U.S. monitoring posts in Iran. But he noted that Brown also said that, even with diminished U.S. intelligence resources, the treaty could be adequately verified from the day it is signed.

"There is no doubt in my mind that this is the case." Carter said. He repeated his pledge that he will "not sign nor present to the Congress nor to the American people any treaty which in my opinion could not be adequately verified from the first day it is effective."

He admitted that there are limitations on what the United States can learn about Soviet missiles.Still, he insisted, "for the Soviets to develop any kind of significant new missile, they would have to have 20 to 50 test launchings. And, during that process, there is every likelihood that we would be able to detect any violation of the SALT treaty."

Although Carter said he believes the accord will win Senate approval, he declared that if it is rejected he would still try to abide by its terms, in order to avoid a new arms race.

"Ide by its terms, in order to avoid a new arms race.

"It would certainly not be proper for me if the treaty were not ratified to immediately launch our country into a massive nuclear arms race," Carter said. "The constraints placed on me and the Soviet Union, monitored very carefully by each other, would be a basis on which to constrain ourselves and to avoid a nuclear confrontation in the absence of a treaty."

The president also denied speculation that he might delay the treaty until election year 1980 to put extrapolitical pressure on the Senate. He said:

"No one has ever seriously considered, in my administration, to my knowledge, any slightest delay in concluding the SALT treaty for political purposes or any other purpose. My understanding is that if it can be concluded fairly early, that it will be considered as a very top priority by the Senate and the action by the Senate will be concluded this year."

On another question of superpower relation, Carter said he favors extending "most favored nation" tariff status to both the Soviet Union and China "if it can be done in compliance with existing law."

That was a reference to four-year-old legislation that ties preferential trade status for certain communist countries, particularly the Soviet Union, to relaxation of emigration policies for Jews. There recently has been a big rise in emigration by Soviet Jews, and the administration is exploring the chances of getting Congress to approve preferred status for the Soviet Union under the law's waiver provisions.

Asked about the possibility of further prisoner exchanges such as last week's trade of five Soviet dissidents for two Russians held here on espionage charges, the President said: "We have not forgotten any human rights activist in the Soviet Union who is being punished or imprisoned."

He said last week's exchange resulted from six months of tedious negotiation "where the Soviets would put forward names and we would assess those names and repeatedly reject them because we did not think they were adequate."

On another foreign policy question, Carter reiterated the U.S. view that Israeli settlements in the occupied West Bank of the Jordan are illegal and counter to the Middle East peace process.

Acknowledging a continuing dispute between the United States and Israel over new settelments. Carter said, "I hope that the Israeli government will severely restrain any inclination, either approved by the Knesset or done without legal sanction, in establishing new settlements. But there is a limit to what we can do to impose our will on a sovereign nation."