West German Chancellor Helmut Kohl says the time has come for the Reagan administration to offer a proposal for an interim agreement that could break the deadlock at the Geneva negotiations with the Soviet Union on medium-range nuclear missiles in Europe.

Kohl also insists that the convincing victory of West Germany's conservatives last Sunday in national elections that featured extended debate on the planned deployment of U.S. missiles here does not lessen the need for immediate progress at Geneva.

In his first extended interview since the election, Kohl said yesterday that despite his determination to improve West Germany's relations with the Reagan administration, Bonn would continue to seek reduced tensions with the Soviet Union.

"We do want disarmament and detente," Kohl remarked, adding that for all Germans, the East-West conflict "is a division cutting right through people's lives, where it's quite normal for two cousins to serve in rival armies, where a brother lives here and a sister lives in Leipzig."

Asked if the Reagan administration should now drop its "zero option" and undertake a new initiative in the Geneva arms talks, Kohl replied that "it certainly is the time for new proposals, but this does not mean we would have to give up the zero solution as an ultimate objective."

Kohl said that his resounding victory at the polls "demonstrated that in our country there is a clear majority in favor of NATO's dual track decision" to deploy modern nuclear missiles later this year if the arms negotiations fail to achieve an agreement.

"We do know that peace and freedom have their price," the 52-year-old chancellor said, "and if serious and thorough negotiations do not lead to anything, then we shall deploy."

"I consider my task to be to stabilize the line of the West. This is why I took this high risk, to have elections now, to put this question up for decision in these elections. And now I have a strong moral position."

In the 90-minute interview in his office here, Kohl also said he intended to use his four-year mandate as chancellor to invigorate West Germany's economy and push hard for new momentum toward European political unity while reviving a climate of warmth and trust with the United States.

His comments on arms control came amid authoritative reports here of an intensifying debate in Washington over the timing and content of a new American proposal, and shortly before a key allied meeting in Brussels where a new strategy may be discussed.

By calling on the United States to introduce a new initiative in the arms talks, Kohl appeared eager to dispel any impression that his government was prepared to give a green light to missile deployment without testing all realistic possibilities of compromise with the Soviet Union.

During his tour of European capitals last month, Vice President Bush said that he was told privately by European leaders that they desired an "interim solution" of low deployment levels of Soviet and American missiles if Reagan's "zero option" plan could not be achieved this year.

That plan calls for the West to cancel deployment of 572 Pershing II and cruise missiles in five Western European countries if the Soviet Union dismantles 600 or more nuclear-tipped rockets aimed at Western Europe.

The allied pressures so far have not produced a change in the administration's publicly stated negotiating stance, but Reagan indicated new flexibility in a recent statement to the American Legion that the administration was willing to explore any proposals put forward by the Soviet Union.

"There is no better aim imaginable for the Europeans to wish for than no missiles for the Americans and no missiles for the Russians," Kohl said in the interview.

" But none of us is living in a world, or a state, where he can say take it or leave it, all or nothing. It's the same thing for the United States. I am very happy that President Reagan used my wording on this point in his speech to the American Legion . Maybe we will have an interim solution, and that's a good thing."

In the wake of Kohl's election, high administration officials said that "much will depend on what position the Bonn government takes on this matter" in determining whether Washington should change its negotiating strategy.

The Geneva talks on intermediate-range nuclear weapons are scheduled to adjourn on March 28. Next Friday, at a consultative meeting of the allies in Brussels, the Europeans are expected to press U.S. Assistant Secretary of State Richard Burt on the urgency of presenting a new American proposal to the Soviets before the current negotiating session goes into recess.

"The German card is a decisive one for the Soviets," Kohl said. "If they realize that they cannot play that card, this will have an effect in Geneva, particularly once the Americans take a step forward."

"The Soviets have another hope now: that there will be a period of unrest in the Federal Republic of Germany," he continued. "Others talk of civil war, but there will not be a civil war, not under this chancellor. There is bound to be anger and friction, but that is politics."

Kohl claimed that the SS20 medium-range Soviet missiles that "are directed in particular at us, provide a broad basis for political blackmail. The Soviets are very clever about exploiting this threat like a carrot and stick."

On domestic matters, Kohl said West Germans need to work harder and save more to revive the economy, for "we have become too fat in the past years; we have to continue changing our economic structure and become more imaginative again."

Kohl recounted a recent dialogue with a Japanese diplomat who suggested to him that Europe had lost its economic dynamism.

"Yes, it's quite true, we have enormous problems, but we are going to come back very quickly in our economy as well as exports," he said. "And the Japanese are going to have to face their problems, for they cannot continue destroying the bay of Tokyo and will have to do something about environmental protection."

Kohl admitted that the antinuclear, ecology-minded Green Party had served a useful purpose by focusing attention during the campaign on the need to cope with West Germany's own environmental problems. But as a political force within parliament, he said, the Greens were likely to "pass away" in the next elections.