Former Presidents urge arms talks

America's retired Presidents have a message for Ronald Reagan: Move quickly on improving relations with the Soviet Union during your second term. ''Time is of the essence,'' Gerald Ford told a gathering at the University of Michigan this week.

Referring to arms control, Mr. Ford said: ''It is important to get started,'' and he expressed hope that the ''harsh rhetoric'' that has been coming from both Washington and Moscow would be toned down. (Konstantin Chernenko called Thursday for strengthening Soviet defenses. Moscow report, Page 2.)

Speaking at the same symposium, on new weapons technology and Soviet-American relations, Jimmy Carter said the Reagan administration ''got off to a bad start'' on arms control during its first term.

But, he added, ''I'm very encouraged by the fact that in an election year - and also since the election - there have been announcements made from the White House that nuclear arms control will be the top priority of this next four years.''

Richard Nixon also is urging Mr. Reagan to set priorities and move quickly during what he calls a ''window of opportunity.'' Mr. Nixon told the Wall Street Journal this week: ''In foreign policy, whether the Middle East, Soviet-American relations, or any change in direction in Central America, the time to do it is right now.''

At the same time, Mr. Nixon said, ''there is too much of a tendency to focus on arms control. . . . You have to look at Soviet-American relations in the broader context of our interests in the Middle East, the Far East, Latin America , and Africa.''

The need to act on foreign policy is apparently very much on the minds of the President and his top advisers, as well. Reagan met Tuesday with Secretary of State George P. Shultz and National-Security Adviser Robert McFarlane to talk about arms control strategy and the broader subject of relations with Moscow.

Administration officials have suggested that the stalled US-Soviet arms control negotiations could be revived under ''umbrella'' talks. These would include the major concerns of both superpowers - in which ''a more philosophical discussion can be held,'' as one senior official puts it.

While acknowledging that ''there are some complexities and limitations'' to be dealt with in reaching an arms accord, Assistant Secretary of State Richard Burt says, ''I think there are some genuine opportunities.''

Experts see several important factors behind a strengthened US hand in dealing with the Soviet Union. Among these are Reagan's clear electoral victory; America's emergence from the ''twin burdens'' (as one former senior official puts it) of Watergate and Vietnam; Washington's strengthened relations with its allies (symbolized by the deployment of medium-range missiles in NATO countries, despite Soviet opposition, and by Japanese jets scrambling this week to ward off Soviet bombers en route to Vietnam); and the internal and diplomatic problems that continue to beset the Soviet Union - succession in the Kremlin, economic difficulties, resistance to Soviet domination in Poland, and prolonged fighting in Afghanistan.

At the symposium in Ann Arbor, presented jointly by the Gerald R. Ford Library and the Carter Center, Lt. Gen. Brent Scowcroft said that ''the Soviet Union is on the strategic defensive.'' Mr. Scowcroft is a retired Air Force general who served as President Ford's national-security adviser and headed President Reagan's Commission on Strategic Forces.

Zbigniew Brzezinski, Scowcroft's counterpart in the Carter administration, said Moscow's problems today ''create the objective preconditions for some accommodation with the United States.'' But, like former President Nixon, Dr. Brzezinski also warned that arms control cannot be isolated from regional crises , urging ''movement on the broad front.''

''It would be a mistake to expect radical changes in (Soviet) policy,'' said former strategic arms adviser William Hyland, now editor of Foreign Affairs magazine. ''But this is a period of opportunity for the United States, where we can have an impact. It is a period where I believe the United States should be more active rather than less.''

In a speech several weeks ago, Secretary of State George Shultz indicated that this might well be the administration's intent.

''The United States is strong and once again comfortable with its role of leadership,'' he told the Los Angeles World Affairs Council. ''The next four years have the potential to be an era of unparalleled opportunity, creativity, and achievement in American foreign policy.'' Major arms initiatives of recent presidents Richard M. Nixon

Interim Offensive Weapons Agreement freezes number of land- and sea-based ballistic-missile launchers. ABM Treaty and Protocol limits each country to one antiballistic missile system. Both signed and ratified as SALT I.

Threshold Test Ban Treaty: Prohibits underground testing of nuclear weapons of over 150 kilotons (signed, unratified).

Summits: Three with Brezhnev. Jimmy Carter

Comprehensive test ban: Negotiations begun to ban all nuclear testing (talks suspended).

SALT II: Sets ceilings on number of strategic missile launchers; limits numbers of multiple-warhead missiles and number of warheads per missile. (Treaty signed, unratified. Both sides have agreed to adhere to treaty provisions.)

Summits: One with Brezhnev. Gerald R. Ford

Vladivostok agreement: Sets up basic framework for SALT II, including principle of 'equal numbers' of launchers for each side.

Peaceful Nuclear Explosions Treaty: Complements earlier Threshold Test Ban Treaty by limiting underground nuclear tests designed for peaceful purposes (signed, but still unratified).

Summits: One with Brezhnev.