President Reagan heads toward the Geneva summit with one of the highest approval ratings of his presidency for his handling of foreign affairs generally and relations with Moscow specifically, according to a Washington Post-ABC News poll.

The poll showed that Reagan's standing got a large boost from his success in dealing with the hijacking of the Achille Lauro. The hijackers of the ship were captured in Italy after their flight aboard an Egyptian airliner was diverted by U.S. Navy jets to Sicily.

The poll also shows that despite oft-expressed distrust of the Soviet Union, Americans have a surprisingly favorable view of the man Reagan will meet at the summit, Soviet leader Mikhail Gorbachev. In this new poll, 39 percent said they have a favorable impression of Gorbachev, while 35 percent said their impression was unfavorable and 26 percent had no opinion.

Other polls have shown that the new Soviet leader has made a better impression on Americans than his predecessors. This has been a source of concern for Reagan, who recently complained that Gorbachev was coming across like a Western businessman in a pin-striped suit.

The survey showed that there is still skepticism about Reagan's proposed missile defense system known as the Strategic Defense Initiative (SDI) or "Star Wars." By 74 percent to 20 percent, Americans say that they would rather have the United States and Soviet Union agree to reduce their nuclear arsenals than for the United States to develop space weapons.

Reagan has made a strenuous effort in recent speeches to describe his vision of the missile-defense system as a space shield that would make nuclear war obsolete. But the poll showed Americans are divided on the merits of the idea. Forty-eight percent said they favored a system that could "guarantee protection" of the United States from incoming missiles, but 46 percent opposed SDI, agreeing with a statement that the system could escalate the arms race and cost many billions of dollars.

Reagan received an overall 63 percent approval rating, almost unchanged from last month. The national telephone poll of 1,506 people was conducted from Thursday through Monday.

On foreign affairs generally, 62 percent said they approved of Reagan's performance, the highest approval recorded by the poll in four years.

Sixty-four percent approved of Reagan's handling of relations with Moscow, the highest rating since the Post-ABC News poll began asking the question in December 1982. Reagan delivered a major address at the United Nations criticizing the Soviets on Thursday, which may have influenced the poll findings, but Reagan had an unusually high approval rating on this point in September and July surveys as well. Before that, Reagan had never been given higher than 56 percent approval and had below 50 percent in several polls.

Americans do not have high expectations for progress on arms control at the Nov. 19-20 summit between Reagan and Gorbachev.

Fifty-four percent of those questioned predicted that the summit will not lead to important accomplishments, while 38 percent said they think that it will.

On the Achille Lauro crisis, 80 percent said they approved of Reagan's actions.

Americans also said they think, by 68 percent to 25 percent, that it is more important to take action against terrorists, such as those who hijacked the Achille Lauro, than to maintain good relations with countries like Italy, according to the poll.

The survey showed that 73 percent disapproved of Egypt's handlng of the hijacking and 57 percent disapproved of Italy's actions. Egypt was criticized by the United States for allowing the hijackers to flee Cairo; Italy for releasing a fifth Palestinian accused of being the "mastermind" of the affair.

Americans appeared skeptical about whether the apprehension of the hijackers would alleviate terrorism. Reagan has warned that the United States will use military force in the future to combat terrorists. But 55 percent said the U.S. actions will not make much difference in the incidence of terrorism; 29 percent said it would decrease terrorism, and 13 percent said it will increase terrorism.

Meanwhile, Reagan's handling of the federal deficit continued to be a concern, with 55 percent saying they disapproved of his actions and 37 percent approving, results roughly similar to those in polls taken over the last two years.