President Reagan, defending his intention to break with the SALT II strategic arms treaty because of alleged Soviet violations, promised last night that the United States will "do our utmost" in the months ahead to draw the Soviet Union into talks on a replacement treaty that would reduce superpower arsenals.

In a nationally televised news conference in which he appeared halting and sometimes confused, Reagan emphasized that the United States will seek to talk to the Soviets about a "definite arms-reduction program" before exceeding the SALT II limits when the 131st B52 bomber is armed with cruise missiles at year's end.

"We're going to see if we cannot persuade them to join in the things they're talking about -- arms reduction," Reagan said. "And, if nothing is done, then we'll make the decision with regard to that plane."

Reagan misunderstood two questions in the half-hour session at the White House. Asked about yesterday's Warsaw Pact proposal for major troop reductions, he responded about a separate Soviet proposal on reducing strategic weapons. Asked about yesterday's Supreme Court decision on abortion, he responded about a decision earlier this week in the "Baby Doe" case.

Reagan said that he "goofed" in a speech this week in which he appeared to liken Soviet leader Mikhail Gorbachev to Cuba's Fidel Castro, Palestine Liberation Organization leader Yasser Arafat and Libya's Moammar Gadhafi. Reagan twice said that Gorbachev is the first Soviet leader "that has ever voluntarily spoken of reducing nuclear weapons."

The president speculated that the explosion of the space shuttle Challenger Jan. 28 might have been due to "the balmy climate off Florida" that made it "difficult for anybody to believe that they'd had a cold snap that . . . could render that O-ring dangerous." Although his top White House advisers are reportedly leaning the other way, Reagan announced that he wants to go forward with building a fourth shuttle orbiter, but he offered no details.

Reagan also reiterated a view he expressed last month that many people are hungry because they lack information about food assistance, but he went further last night, saying, "I find it difficult also to find any cases of starvation and undernourishment." A number of private studies have reported that there is a growing hunger problem among Americans.

On arms control, Reagan was asked about his May 27 announcement that the United States is abandoning SALT II. The announcement caused protests from U.S. allies and critics in Congress that Reagan was giving up on a treaty that, although never ratified by the Senate, had helped prevent an unrestrained weapons buildup.

At that time, Reagan said he would no longer base U.S. military decisions on the "flawed SALT II treaty" and that he intended to deploy a B52 bomber in a way that would exceed the numerical limits of SALT II near the end of this year. But Reagan then appealed to the Soviets to use the months ahead "to take the constructive steps necessary to alter the current situation" and said that if that is done, "we will certainly take this into account."

Last night Reagan emphasized his intention to try and draw the Soviets into talks about a replacement treaty for SALT II, saying that the Soviets have "an opportunity to meet us now" on arms reductions.

At one point Reagan was asked why he had decided now to abandon SALT II. He went so far as to say, "I didn't make it now. I said we've got several months to try to involve them the Soviets in things they, themselves, have been talking about and that is a definite arms-reduction program."

As in his May 27 announcement, however, Reagan did not say explicitly what he is asking the Soviets to do or what response he would be prepared to make. A senior U.S. official in the arms control area said there is no consideration being given within the administration to changing the decisions announced May 27.

Commenting on Reagan's remarks, Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) said last night he thinks that the president was deliberately keeping his options open. "I think the president was obviously trying to avoid" being pinned down about exceeding the SALT II limits, he said. "He was saying the door is open if there is a change" in Soviet behavior, he added.

Senate Minority Leader Robert C. Byrd (D-W.Va.), however, had a different interpretation of Reagan's words. He said, "The president has heard our allies and Congress. He has said a decision on SALT II has not been made. His advisers should take a cue from the president. The rhetoric on killing the current restraints should end."

Reagan last night did not reject out of hand a new Soviet arms control offer, which was broached in the Geneva talks May 29 and was formally presented by Soviet negotiators in Geneva yesterday. "We don't know yet until we see it carefully" whether some or all of it could be acceptable to the United States, he said.

Officials said active discussions are taking place within the administration about the Soviet proposal, which is reported to call for large cuts in offensive strategic arms in return for U.S. adherence to the 1972 Antiballistic Missile Treaty for 15 to 20 more years.

Reagan also expressed confidence last night that there will be another summit meeting with Gorbachev, but he did not predict that it would be this year.

Opening the 37th nationally televised news conference of his presidency, Reagan again warned against making what he called "large and dangerous cuts" in the defense budget and vowed to veto any tax increase. He also praised the version of tax-overhaul legislation pending in the Senate and called on Congress to approve his request for $100 million to support the rebels fighting the Sandinista government of Nicaragua.

"Delay on the aid request is deadly and plays right along with the communist game plan" to wipe out the resistance, he said.

Earlier yesterday, a White House spokesman, Edward P. Djerejian, announced that the administration has obtained evidence showing that a Soviet AN30 photo reconnaissance plane was identified in early May at the Sandino airport in Nicaragua. "The aircraft carried Soviet Aeroflot markings and presently is being flown by Soviet pilots," he said. "This is the first time that a Soviet photo reconnaissance plane has been based in Nicaragua. Such aircraft are capable of photo reconnaissance and photo mapping operations.

"Both such missions would be of assistance obviously to the Sandinistas in their counterinsurgency operations" against the contras, or counterrevolutionaries, he added. The plane has flown four missions since it has been in Nicraragua, he said. The announcement is the latest the White House has made about Soviet aid to the Sandinistas as part of a campaign to win the congressional battle over aid to the rebels.

In a speech Monday discussing the rebels, Reagan had said, "Just as the men and women of the resistance have decided what they must do, so, too, have Gorbachev, Castro, Arafat and Gadhafi." Asked last night what effect the comment would have on the next summit with Gorbachev, Reagan said, "I didn't think I lumped him in with them." When informed he had, the president added, "it was a bad choice of words, because I didn't mean to do that. . . . So I must have goofed some place, because believe me, I don't put him in the same category."

Reagan apparently had trouble concentrating on the next question about yesterday's Supreme Court decision on abortion, telling the questioner, "Hit me again here." He then misunderstood the query and talked about a court decision on the "Baby Doe" case.

The president was also questioned last night about contradictory statements from the State and Justice departments over the Pollard spy case and the extent of possible Israeli spying against the United States.

Reagan said "the only thing I know" is that Israel has "assured us as much as they can that they have never had any program of trying to get intelligence information from our country or doing any spying on us." While the Justice Department is conducting a further investigation, he said, "there's been no evidence presented to us from anyone" of additional espionage, and if such evidence is found, "we'll have to deal with that then, and find out whether it's a surprise to the Israeli government, whether someone was off playing their own game or not."

Also last night, the president said he agrees with former secretary of state William P. Rogers, chairman of the commission that investigated the space shuttle accident, that individuals should not be punished for the disaster, which killed seven astronauts.

"I don't believe that there was any deliberate or criminal intent in any way on the part of anyone," Reagam said. He blamed the accident on "complacency" at the space agency, saying that "it was just a carelessness that grew out of success."

"Maybe part of it was also due -- I've often wondered this: if part of it wasn't due to the balmy climate of Florida and that it was difficult for anybody to believe that they'd had a cold snap that was -- that could render that O-ring dangerous," he said.

Asked about reports of racial discrimination at the Agriculture Department, Reagan said Secretary Richard E. Lyng is investigating them and is determined to correct any wrongs.Staff writers Helen Dewar and Don Oberdorfer contributed to this reoport.