MOSCOW, FEB. 25 -- President Reagan is expected for a summit meeting in the Soviet Union during the last week of May, according to a senior Soviet official who also said he expects that a treaty to reduce the superpowers' strategic arms stockpiles will be ready for signing then.

The official said Reagan will stay in the Kremlin during the visit, the first meeting between U.S. and Soviet leaders to be held in the Soviet capital in 14 years. He said the visit should last for about a week and could include other cities.

The official stressed that after talks with Soviet leader Mikhail Gorbachev, Reagan would be free to travel anywhere he wanted in the Soviet Union.

As the official outlined it, Reagan's trip will be more extensive than Gorbachev's journey to the United States in December. Gorbachev stayed for only three days, chose to live in the Soviet Embassy in Washington and did not travel out of the capital.

During a two-hour meeting with about 20 foreign reporters, the senior official also outlined new Soviet policy positions on a wide range of issues, including contingency planning should heavy fighting continue between resistance fighters and government troops in Afghanistan following the withdrawal of Soviet forces, and plans for reestablishing diplomatic ties with Israel.

The Washington Post, which was not invited to the briefing, obtained details of the official's remarks from reporters who were present.

Under a timetable announced by Gorbachev earlier this month, the Soviet pullout from Afghanistan will begin May 15 if Geneva negotiations on the Afghan war result in a treaty by mid-March.

Gorbachev said that the withdrawal would continue for 10 months. But the official said today that the Kremlin is aware that a blood bath could occur in Afghanistan during that period and has devised plans for such a scenario. He said the Soviet Union would favor a United Nations presence as part of a plan to help keep the peace, according to Reuters.

While defending the original decision to send Soviet troops to Afghanistan in 1979, the official criticized Soviet leaders for continuing the war.

The official also said that Moscow is prepared to resume diplomatic relations with Israel on the first day of a proposed Middle East peace conference, ending a rupture that began in 1967. Ties between the Soviet Union and Saudi Arabia would be restored at the same time, he said.

Moscow is seeking to shore up its relations throughout the Middle East and to pressure the United States and other countries to agree to a conference that would include both superpowers and bring the Soviets back into the center of Mideast diplomacy.

Washington has launched its own attempt to end fighting and strengthen its ties in the region.

During today's briefing, held two days after Secretary of State George P. Shultz ended talks here, the official emphasized that U.S.-Soviet relations have reached a new plane and are concentrated on mutual goals rather than confrontation.

Relations have been hampered in the past by Soviet objections to the Reagan administration's plans to build a space shield against nuclear weapons, but Moscow's attitude toward the U.S. program has evolved, the official said.