Ronald Reagan restated old foreign policy ideas in a new conciliatory tone today during a speech on the eve of the Illinois primary that was designed to show that he is not a warmonger.

Reagan's speech to the Chicago Council on Foreign Relations had been billed as "major foreign policy address" by Reagan adviser Richard V. Allen. The Reagan strategists thought so highly of the speech that they distributed a text for only the second time in the campaign, and Allen briefed reporters beforehand.

But almost all of the ideas expressed had been voiced by Reagan many times before, especially in a Feb. 15 speech at Worcester, Mass.

Reagan accused the Carter administration of pursuing a foreign policy of "vacillation, appeasement and aimlessness." He called in general terms for foreign policy based on "a clear vision of America's future," a strong economy, and a military buildup that would give the United States "the unquestioned capability to preserve world peace and our national security."

What was new today was Reagan's stress on the arms negotiations he said must arise from the buildup.

". . . We cannot negotiate arms control agreements that will slow down the Soviet military buildup as long as we let the Soviets move ahead of us in every category of armaments," Reagan said. "Once we clearly demonstrate to the Soviet leadership that we are determined to compete, arms control negotiations will again have a chance. On such a basis, I would be prepared to negotiate vigorously for verifiable reductions in armaments, since only on such a basis could reductions be equitable."

Reagan frequently has stressed his opposition to the unratified strategic arms limitation treaty (SALT II), saying that it would give the Soviets a military advantage over the United States.

In preparing for today's speech, Reagan assembled his senior staff and a group of seven outside advisers headed by former arms control agency director Fred C. Ikle for a three-hour meeting at the Altanta airport on March 10.

But the content of today's speech may have been determined in part by survey findings in the Illinois primary showing that some potential Republican voters are concerned about Reagan's hawkish international views.

The bland, unspecific nature of the speech also may have been influenced by a perception in the Reagan camp that the former California governor is now ahead in Illinois and shouldn't make waves.

One section of Reagan's speech raised the specter of Soviet domination of the Caribbean, where the candidate said that "totalitarian Marxists" control the island of Grenada. Reagan said the Cuban advisers on that island "are now training guerrillas for subversive action as in Trinidad and Tobago, Grenada's democratic neighbor."

"Must we let Grenada, Nicaragua, El Salvador, all become additional 'Cubas,' new outposts for Soviet combat brigades?" Reagan continued. "Will the next push of the Moscow-Havana axis be northward to Guatemala, then to Mexico, south to Costa Rica and Panama?"

Reagan never did answer these questions. Nor would he give specifics on what he thought the U.S. military budget should be or on the weapons systems that this country should develop. When a questioner at the Foreign Relations Council asked for specifics on the military budget, Reagan replied, ". . . In national defense you have to spend whatever is necessary to deter the enemy."

In the briefing before the speech, Allen said that specifics will be forthcoming sometime in the spring as Reagan develops foreign policy alternatives to Carter's.

While Reagan has been trying to soften his foreign policy image, fading candidate George Bush has been trying to sharpen his. Before this same audience last Friday, Bush took a tougher line than Reagan did today, denouncing the administration for a policy of "bluff, bluster and political symbolism," and declaring that Carter should break off relations with Iran, close the Iranian embassy and define its policy towards Iranian nationals in this country.

Bush also gibed at Reagan's view expressed earlier that the Iranian militants should be given a deadline for release of the hostages, and that the United States should take an unspecified "unpleasant action" if the deadline is not met.

"Let's call it the Reagan secret plan for ending the Iranian hostage crisis."