Soviet President Yuri Andropov met Chancellor Helmut Kohl today for "hard but constructive" talks, a day after suddenly canceling two sessions for health reasons, according to sources in the West German leader's delegation.

The West German sources said they believe yesterday's postponement was due to a kidney ailment and that Andropov's rapid recovery was due to dialysis treatment. The Soviet leader, 69, reportedly looked physically weak, but Bonn officials stressed that he was mentally alert and spoke clearly without using notes.

Andropov warned Kohl that "the military threat for West Germany will grow manifold" if new American nuclear missiles are deployed there later this year.

During three hours of talks at the Kremlin, Andropov hinted that Moscow would retaliate by installing new rockets in Eastern Europe and said he found it "hard to understand" what Bonn hopes to gain "from the oversaturation of Central Europe with all types of weapons of mass destruction."

Despite the harsh rhetoric, West German officials sought to depict some signs of flexibility in Soviet positions on arms control and a possible East-West summit.

After telling Andropov that he felt it was vital for "the two most important men in the world" to meet soon, Kohl told reporters that the Soviet leader responded favorably but then added that any summit with President Reagan "should be carefully prepared and not serve as a propaganda exercise."

"This is exactly how Washington feels about the subject," Kohl said.

The West German chancellor also said he was pleased that Andropov expressed keen interest in reaching a compromise at the Geneva talks on medium-range nuclear missiles before new Pershing II and cruise missiles are to be installed in Western Europe starting this December.

"Even though our positions are quite distant, we both agreed that it is not too late to achieve an agreement," Kohl said.

Senior aides to the chancellor said they found it positive that Andropov "did not contradict" Kohl's assertion that negotiations should continue even if the West proceeds to deploy new missiles.

"The Soviets have been shifting their positions in several areas of arms control, so why not in Geneva?" said one of Kohl's top foreign policy advisers.

But the official Tass news agency quoted Andropov as saying it was "a profound and dangerous delusion" to believe the Soviet Union would offer concessions in Geneva after new U.S. missiles are brought to Western Europe. The U.S. position has been that going ahead with plans to deploy the missiles is the only way to negotiate from a position of strength with Soviets.

Kohl's spokesman, Peter Boenisch, said that Andropov seemed "clear and alert" during both sessions today, displaying intellectual command of the issues and occasional flashes of wit.

According to a West German source present at the talks, Andropov kept his left hand "numb and stiff" when the two leaders met over a green baize conference table. During opening remarks, Andropov raised a trembling right hand in an apologetic gesture.

"It was my deepest wish to see you Monday , but unfortunately it was not possible. I was sick," Andropov was quoted as saying.

"In politics there are always such barriers, and I fully understand," replied Kohl.

"Then we have agreed already on one question," Andropov quipped.

West German officials claimed success for Kohl's visit to Moscow because the Soviets seemed to share their view that long-term relations in trade, cultural and other fields should not deteriorate because of the missiles controversy.

But they conceded that Kohl failed to budge the Soviets from their insistence that French and British nuclear deterrent systems must be counted in any assessment at Geneva of the East-West missile balance.

The conflict over French and British systems is considered the main stumbling block to progress in the Geneva negotiations. Even so, West German officials said they were surprised at how the topic dominated so much of the discussions.

Boenisch said Kohl told Andropov that "we in the West are not suicidal missile addicts" and that the 572 new missiles scheduled for deployment are designed to counter the Soviet arsenal of nuclear-tipped rockets aimed at Western Europe.

Kohl described British Prime Minister Margaret Thatcher and French President Francois Mitterrand as "peace-loving" and said "it would be grotesque" to think that they would use their countries' minor nuclear systems to attack the Soviet Union.

Kohl said he rejected any possibility of launching a war. He stressed that because Bonn has renounced nuclear weapons, it must depend entirely on "the American nuclear umbrella."

Tass quoted Andropov as saying the western position "boils down to the demand for unilateral disarmament of the Soviet Union" and added that "we cannot disregard, in particular, the considerable quantities of British and French nuclear weapons aimed at us."

If it comes to deployment, Andropov continued, "We will neither surrender our positions nor weaken our defense but take prompt and effective measures in response to ensure the security of the Soviet Union and its allies."

On other East-West issues, Soviet and West German delegations hailed an apparent breakthrough in the Madrid conference on security and cooperation in Europe. The three-year negotiations have been stymied by differences about human rights issues.

West German Foreign Minister Hans-Dietrich Genscher proposed to his Soviet counterpart, Andrei Gromyko, that all foreign ministers of participating countries should go to Madrid to sign the final agreement, which may be ready as early as July 15. Gromyko promptly agreed, West German officials said.