President Reagan and Democratic presidential nominee Walter F. Mondale attacked each other's world views and foreign-policy positions along a broad front in last night's debate, and flatly disagreed on several controversial questions that have been the subject of much public comment.

Reagan defended his administration's actions and policies in Central America, Lebanon, the Philippines and above all on arms control, and charged Mondale with seeking "unilateral disarmament" and courting "policies of weakness."

Mondale attacked Reagan as a leader with singular lack of success in arms talks with the Soviet Union who had not been able even "to master their essential elements," and who presided over serious setbacks in Central America and the Middle East.

Some of their disputes came over how well Reagan grasps essential facts about the nuclear weaponry under his command.

Mondale, alluding to a charge frequently heard on the campaign trail, attacked Reagan for believing that submarine-launched nuclear missiles can be recalled after they are launched. The president responded that, "I never, never conceived of such a thing. I never said such a thing."

The Democratic charge arose from Reagan's statement about his first strategic arms control proposal at a news conference, four days after it was announced in May 1982. On that occasion he spoke first of land-based missiles, of which he said there was "no recall" and "no defense." On the other hand, he added, "those that are carried in bombers, those that are carried in ships of one kind or another, or submersibles, you are dealing there with a conventional type of weapon or instrument, and those instruments can be intercepted. They can be recalled if there has been a miscalculation."

Another issue concerned Reagan's knowledge of Soviet nuclear forces at the time of his initial strategic arms proposal. Mondale charged that Reagan discovered after three years that "our arms-control efforts have failed, because he didn't know that most Soviet missiles were on land."

Reagan explained, in response to a question, that "to our surprise and not just mine" the Soviet Union made it plain following the initial proposal that it placed "a greater reliance on the land-based missiles" than on other types. The president went on to say "it was a surprise to us" because the Soviets also outnumbered the United States in submarines and nuclear-capable bombers.

Reagan was quoted by The New York Times in 1983 as having told members of Congress he did not realize at the time of his May 1982 proposal that the Soviet Union has 70 percent of its strategic nuclear warheads on land. The Reagan proposal would have required such forces to take the heaviest cuts.

Another issue in nuclear-weapons negotiations that was contested by the candidates last night was whether the Reagan administration or the Soviet Union was responsible for rejecting the so-called "walk in the woods" formula developed in Geneva in 1982. This was a proposal informally suggested by U.S. Ambassador Paul H. Nitze to his Soviet counterpart in an effort to break the deadlock in Intermediate-Range Nuclear Forces (INF) negotiations.

According to "Deadly Gambits," a book by Time magazine correspondent Strobe Talbott that took a detailed look at Reagan arms-control policy-making, Nitze's plan was rejected by Reagan at the insistence of civilian Pentagon officials during a National Security Council meeting on Sept. 13, 1982. Subsequently the Soviet Union passed word, apparently independent of Washington policy-making, that it rejected the Nitze plan also.

Considerable debate last night was centered on Reagan's 1983 Strategic Defense Initiative, popularly dubbed the "Star Wars" plan to stop in-flight missiles aimed at the United States.

Reagan explained what he had in mind on March 29, 1983, when he suggested that a future president might share the sophisticated defense technology with the Soviets.

"My idea would be" that if and when the defensive shield were created, "we would sit down with them the Soviets and then say, 'Now are you willing to join us?' " Reagan said. He added that he would "give them a demonstration" and offer to share the defensive weapon "if you're willing to join us in getting rid of all the nuclear weapons in the world."

In response to a follow-up question, Reagan said he had not discussed his plan for eventual discussions with the Soviet Union with members of the Joint Chiefs of Staff, but that "it seems to me that this could be a logical step" toward the elimination of nuclear weapons. He and Mondale agreed that such a "Star Wars" defense is far from a reality, though Reagan discussed it with a much greater degree of optimism.