President Reagan warned yesterday against "wishful thinking or public-relations campaigns" in advance of the November summit with Soviet leader Mikhail Gorbachev and said he intends to remind Gorbachev of "why we believe they represent a threat to us and to the Western world."

Reagan said he hopes the Geneva meeting with Gorbachev will demonstrate to the Soviets "by deed, not word, that we are not an aggressor."

The remarks were the first detailed response Reagan has made to an intensifying Soviet public-relations campaign in advance of the summit, including Gorbachev's charge in an interview with Time magazine that the United States is planning a confrontation in Geneva.

Vice President Bush predicted in a speech this week that serious negotiations with the Soviets may follow an intensive propaganda campaign. Yesterday, in welcoming Danish Prime Minister Poul Schleuter to the White House, Reagan said the summit could be "a beginning point for better relations -- a starting point for progress."

Also yesterday, Reagan received a report from a group of senators led by Minority Leader Robert C. Byrd (D-W.Va.) on their recent meeting with Gorbachev.

Sen. George J. Mitchell (D-Maine) said afterward he thinks that the "essential elements" of an arms-control agreement with the Soviets are becoming "increasingly clear." He said this would be a trade-off of deep reductions in Soviet offensive missile forces in exchange for "some level of restraint on strategic defense systems."

Mitchell said there is not enough time before the summit for a detailed agreement but that he hoped Reagan and Gorbachev could "break the impasse" on these issues, including "some restraint" on the Strategic Defense Initiative as part of the deal for deep cuts in Soviet missiles. But Reagan "did not respond," the senator said.

In an interview Monday with a college radio network, which the White House made public yesterday, Reagan was asked about his goals for the Nov. 19-20 meeting.

Saying the superpowers "hold so much of the fate of the world in their hands," Reagan responded:

"Now if the Soviet Union, in all of its talk that we represent a threat to them, that we are the aggressor and so forth, if there is any element of real belief in that, if that isn't just propaganda and they really believe that, then I would like . . . to talk a little bit, well, or give them facts to try and show them by deed, not word, that we are not an aggressor.

"On the other hand, at the same time I would like to reveal to them why we believe that they represent a threat to us and to the Western world. There is their expansionism in Africa, Ethiopia, the Cuban troops that the Soviet Union is maintaining . . .[in Angola]," he said. He also cited Afghanistan.

He said "every Russian leader" has "over and over again restated their goal of a one-world socialist revolution, a one-world communist state. And, invariably, they have declared that the United States is the final enemy.

"I know that we have differences," Reagan said. "We're not going to like their system. They're not going to like ours . . . . we're not out to change their system. If that's what they want, let them go forward with their foolishness."

Reagan said the Soviet arms buildup has so reduced standards of living that the average Soviet citizen spends more time waiting in line at stores than working.

He also said that, given a chance, he would tell the Soviet people that the United States bears no "enmity" toward them "but that their government policies, their expansionism has led us to fear them."

Of his second-term goals, Reagan said: "First of all, with the arms talks, maybe it might be impossible; I don't know. But I would like to see the end of nuclear weapons. I would like to envision the Soviet Union and the United States agreeing, and then verifiably eliminating those weapons, and then being able to turn to lesser nations or other nations that maybe have some and saying, 'Look, we've done this now. Come on, get in line. You do it, too. Let's rid the world of this nightmare and this threat.' But that'll be something we'll continue to try to do."