President Reagan said in an interview with news agency correspondents yesterday that he had been misunderstood when he remarked that his space-based missile defense system will not be deployed until all nuclear missiles are eliminated.

Reagan said he would still seek elimination of nuclear weapons in talks with the allies and Soviets about sharing the strategic defense system. He added that if the Soviets refused to go along, "we would go ahead and deploy" it. But he expressed optimism at the same time that "any nation offered" the strategic defense system would "see the value of going forward" with it.

Earlier in the day, Reagan responded "hell, no" when asked whether he would give the Soviets veto power over the Strategic Defense Initiative, his proposed "shield" against incoming ballistic missiles now in the research phase.

In his comments, the president said firsthand what his spokesman and others had been saying earlier: He had not intended to outline sweeping changes in his policy on the defense system when he discussed it in an interview with Soviet journalists on Monday.

Speaking to correspondents from the Associated Press, United Press International, Reuters and Agence-France Press, Reagan also suggested that there could be a pattern to three recent, apparent defection attempts -- the Soviet sailor who twice jumped into the Mississippi River, the young Soviet soldier who took refuge in the U.S. Embassy in Afghanistan and the case of KGB official Vitaly Yurchenko.

"I have to say that this -- coming as they do together -- these three particular incidents, you can't rule out the possibility that this might have been a deliberate ploy or maneuver," Reagan said.

But Reagan also noted that "in every one of the three incidents, we insisted on and did secure the last word . . . to make sure that they understood completely that they were welcome here . . . . "

The president said he will use the Nov. 19-20 summit with Soviet leader Mikhail Gorbachev to "try to impress upon them how firmly we believe in this." Reagan said, "flexibility, I think, is not involved" in the discussions with Gorbachev.

Reagan said he did not foresee detailed negotiations on arms control at Geneva. "I don't think the negotiation of facts and figures about which weapons and how many and numbers and so forth in weaponry should take place at the summit," he said.

"I think that belongs where we've already put it and that is with the arms control negotiators that are already in Geneva. That's their kind of figuring that should go on. We shouldn't be doing that, with all of the things we have to discuss at the summit meeting."

Reagan said his major goal at Geneva is to come up with "guide tools" that would be used to "eliminate the distrust" between the superpowers and "the other things would automatically follow."

The president was also asked to respond to a remark Gorbachev made to U.S. officials in Moscow this week, including Secretary of State George P. Shultz, that American policy was influenced "by a small circle of anti-Soviet extremists."

Reagan said he would tell Gorbachev that "if this were true, that the United States were guided by some desire to one day assault the Soviet Union, why didn't we do it when we were the most powerful military nation on Earth, right after World War II?"

Reagan said he wanted to contrast this with Soviet behavior, that "their expansionist policy is very evident. The gunfire hasn't stopped for a moment in Afghanistan . . . . So this is my hope, that I can convince him, if he's a reasonable man, and there's every indication that he is, would see if we both want peace, there'll be peace."

On other topics, Reagan said:

*"You can't rule out the possibility that this might have been a Soviet decision to allow Yelena Bonner, wife of Soviet dissident Andrei Sakharov, to get medical attention in the West is "long overdue." But Reagan said human rights, while a summit topic, should be discussed "privately and quietly" with the Soviets because that is how "the greatest success" has been achieved.

*The administration has had discussions "at a ministerial level" with the Soviets on reducing the number of Soviet and Eastern European diplomats in the United States, but "we recognize" the result may be retaliation by Moscow.

*"I have had a good recovery" from cancer. Reagan took issue with reports of his illness that have portrayed him as "the sufferer of cancer." He said, "I had cancer.