President Reagan intends to push research on a ballistic-missile defense system even if an agreement is reached with the Soviet Union on reducing or eliminating nuclear weapons, he said in an interview published yesterday.

Speaking to The New York Times, Reagan also said he would not trade research on his Strategic Defense Initiative, also known as "Star Wars," for deep reductions in Soviet offensive nuclear weapons.

The Soviet news agency Tass criticized his remarks yesterday, saying that they show that the United States does not intend to bring a realistic attitude to arms negotiations scheduled to resume in Geneva next month, Reuter reported.

Sen. Charles McC. Mathias Jr. (R-Md.), who returned Sunday from a week of talks with top Soviet officials, including Foreign Minister Andrei A. Gromyko, said yesterday that Moscow believes the missile-defense system is a threatening "sword" and "a cover for a first-strike capability."

Mathias said the Soviets want research in the program "terminated" if there is to be progress in the other areas of U.S.-Soviet arms-reductions talks: intermediate-range missiles and long-range strategic weapons.

But Reagan's remarks appeared to underscore the U.S. position that the missile-defense system is not a bargaining chip. Asked if he would trade his initiative for deep reductions in Soviet offensive weapons, Reagan said:

"No, I would want to proceed with what we're doing, which is research to discover whether there is such a weapon and whether it is practical and feasible. And then I, myself, have said that my own view would be that if that is determined and there is -- we can produce such a weapon, that then before deployment, I'd be willing to sit down and, in a sense, internationalize . . . . "

Reagan added that he would "negotiate then before there would be any deployment or anything to make sure that they understood that we weren't trying to create the ability of a first strike our- selves . . . . "

Administration officials have repeatedly said a decision on whether to deploy a strategic-defense system would be made by Reagan's successor.

Reagan said a missile-defense system would be "well worth having" even if nuclear weapons are sharply curtailed. He compared it to use of gas masks to combat poisonous gas in World War I, saying a defensive system could knock out missiles "just as today you could put on the gas mask if somebody cheats and decides to use poison gas."

The president said there is currently "no defense whatsoever" against nuclear missiles. "The only program we have is MAD -- Mutual Assured Destruction. And, why don't we have MAS instead -- Mutual Assured Security?" he asked.

Questioned about whether such a missile defense would protect entire cities or just missile silos, he said, "I want a defense that simply says that, if somebody starts pushing the button on those weapons, we've got a good chance of keeping all or at least the bulk of them from getting to the target . . . . I don't think of it in terms of let's put it around this place or that place. Let's put it in such a way that those missiles aren't going to get to their target."

Asked how alleged Soviet treaty violations will figure in the forthcoming negotiations, Reagan said he will insist on a "verifiable" agreement. "All of these" violations, alleged by the administration, "will be part of the negotiations," he said.

Saying U.S. missile-defense research does not violate the 1972 anti-ballistic missile treaty, Reagan asked rhetorically of the Soviets, "Who are they kidding? They've been conducting research in this sort of thing for a long time. And they already have, far beyond anything we have, and we believe, in violation of the ABM Treaty, that kind of defense."

Reagan said that "we have not completely caught up with" the Soviets in military might but that the United States will enter the negotiations with "a little more realism than there's been in the past" because the Soviets "know that there's been a change of attitude, that we are not canceling weapons systems and -- without getting getting anything in return."

On other topics, Reagan said "there was bad judgment on both sides" in the fracas involving South Korean security agents and Americans at Seoul airport when South Korean opposition leader Kim Dae Jung returned there last week.

He also said the United States "should continue to offer support to the people of Nicaragua who have been betrayed in the revolution that they, themselves, supported," referring to the rebels fighting the Sandinista government of Nicaragua. Congress has shut off U.S. aid to the rebels.

"I still believe in covert programs where they're necessary and where they're desirable," Reagan said, declining to be more specific.

Reagan also said:

* That he is "not greatly optimistic" about improving relations with Cuban President Fidel Castro because "their words are never backed by deeds."

* That the trial and conviction of four Polish police officers in the murder of a Roman Catholic priest do not represent a change by the Polish government.

"I honestly don't think it reflects any change," he said. "I think it reflects something that went wrong. And the government doesn't mind throwing somebody to the wolves in order to keep the sleigh going ahead of the wolf pack."

* That he is "just not going to think about" whether he will endorse Vice President Bush for the 1988 Republican presidential nomination because the party has to "make its decisions." But he added that voters would have to consider Bush's experience in the administration.