President Reagan moved to seize the initiative on arms control yesterday before his Nov. 19-20 summit meeting with Soviet leader Mikhail Gorbachev by presenting what he called a "serious and detailed" new plan for reducing nuclear arsenals.

On a busy day of presummit moves and countermoves, administration sources also disclosed that Secretary of State George P. Shultz will propose to Gorbachev next week that the superpowers hold a follow-up summit next year and consider convening annual summit meetings.

A plan for annual summits has been vigorously advocated by allied leaders, who believe a regular superpower meeting would ease world tensions and improve East-West understanding.

Shultz leaves Saturday for discussions in Moscow that he predicted would be "businesslike and constructive."

While Reagan and Shultz looked forward to a summit that was described optimistically by the president, Defense Secretary Caspar W. Weinberger told the Senate Foreign Relations Committee that the administration has rejected a Soviet proposal to halt construction of a giant new radar in central Siberia.

The Soviet offer was contingent on the U.S. ceasing modernization of radar sites in Greenland and Britain. Weinberger said the proposal equates a Soviet project prohibited by the 1972 Antiballistic Missile (ABM) Treaty with U.S. improvements that the treaty permits.

Reagan appeared in a crowded White House briefing room yesterday afternoon to announce that the new U.S. arms control proposal will be submitted in Geneva today hours before negotiators are scheduled to recess the third round of the superpower nuclear arms talks.

The president asked Moscow for a week's extension of the talks so the Soviets could examine the plan.

While the president provided no details, administration officials said the proposal accepts the "concept" of a Soviet plan that would reduce strategic nuclear arsenals by 50 percent. But it redefines the concept by excluding medium-range U.S. bombers and missiles from the total of strategic warheads.

Sources said the U.S. plan would reduce strategic arsenals on both sides to a maximum of 4,500 nuclear warheads and place a limit of 3,000 warheads on Soviet land-based intercontinental ballistic missiles (ICBMs), the heart of the Soviet strategic force.

Administration sources said the U.S. proposal would also place limits on its bombers, air-launched cruise missiles and submarine-based missiles, including the D5 missile now under development and also known as the Trident II.

Those limits were not disclosed.

The D5, which could be armed with up to eight nuclear warheads, has drawn particular attention from the Soviets because of its great firepower and accuracy.

It is believed to be the first submarine-launched missile potentially capable of destroying a land-based ICBM within a hardened silo.

The Soviets strongly criticized an earlier U.S. proposal for reducing strategic arsenals because it omitted bombers and air-launched cruise missiles, categories in which the United States has a large lead.

Reagan said yesterday that the United States was not seeking the capability to launch a nuclear "first strike" against the Soviet Union.

Limiting the D5, which is scheduled to have its first flight test in 1987, would support this statement by restricting U.S. first-strike capability, U.S. officials contend.

The president said he would "characterize our arms control position as deep cuts, no first-strike advantage, defensive research -- because defense is safer than offense -- and no cheating."

Reagan had been scheduled to announce the new plan today at the same time U.S. negotiators were presenting it to their Soviet counterparts.

Officials said the president advanced his timetable after the proposal was disclosed Thursday in The Washington Post.

In announcing the plan, Reagan said he hoped it would "enable both of our nations to start moving away from ever-larger arsenals of offensive forces."

At the same time the president reiterated his commitment to his proposed space-based missile defense, the Strategic Defense Initiative.

"We seek in Geneva to undertake with the Soviets a serious examination of the important relationship between offensive and defensive forces, and how people everywhere can benefit from exploring the potential of non-nuclear defenses," Reagan said.

The Soviet proposal for a 50 percent reduction in strategic forces also called for severely restricting the Strategic Defense Initiative program, often called "Star Wars."

U.S. officials said the new U.S. proposal deals only with offensive weapons and offers no concession to the Soviets on limiting testing and development of a defensive system.

In his testimony yesterday, Weinberger said he "wouldn't want to give up strategic defense in any circumstance."

At a news conference yesterday, Shultz outlined U.S. preparations for Geneva and emphasized, as Reagan did at the United Nations last week, that the United States wants summit discussions to include regional conflicts, including those in Afghanistan and Nicaragua, and human rights issues, as well as arms control.

The secretary of state said there was a positive climate between Washington and Moscow in the summit preparations, "more of an atmosphere of exchanging views on these subjects back and forth than there has been in quite awhile."

"Whether it will lead to something remains to be seen," he added.

Shultz also gave the first official U.S. confirmation of a report that Yelena Bonner, wife of Nobel Peace Prize laureate Andrei Sakharov, has been given permission to leave the Soviet Union for medical treatment.

Permission for this move, long sought in the West, has been interpreted as a sign of Soviet flexibility in advance of the summit.

Shultz said that "I understand that Mrs. Bonner will be free to leave the Soviet Union," information he said came from a Soviet official.

While Shultz did not identify the official, he met Tuesday with Soviet Ambassador Anatoliy Dobrynin.

Despite his generally positive attitude toward the summit and his upcoming meetings with Soviet officials, Shultz was unyielding in expressing U.S. opposition to the Soviet-supported Sandinista government in Nicaragua. The secretary of state enumerated civil liberties violations in Nicaragua and said the Sandinista government had "unfortunately declined" to discuss them.