West Germany's opposition candidate for chancellor, Hans Jochen Vogel, said today that the Soviet Union was prepared to negotiate on the number of warheads, not just the number of intermediate-range missiles in Europe.

Reporting on talks with Soviet leader Yuri Andropov in Moscow this week, Vogel told a press conference that the Soviets were willing to destroy some of their missiles targeted on western Europe--a position he had alluded to earlier this week--and to seek a balance that would take into account numbers of warheads as well as of missiles deployed by both sides. He said the United States should follow up this initiative.

U.S. diplomats said the apparent Soviet change could be significant because it would mean that Moscow was "moving in the right direction of measuring actual balances and not just missiles" and thus accepting Washington's view on the key matter of arms control criteria. Western nations have reported diplomatic efforts in Moscow to seek further details of the announced Soviet initiatives, including those for the Euromissile talks in Geneva.

The issue of adopting less rigid positions to reciprocate Soviet gestures has become a source of controversy here as West German parties begin battling for votes in national elections scheduled for March.

Vogel's Social Democrats have enhanced their standing in polls as the party best suited to mediate between the superpowers and his highly publicized visits to Washington and Moscow were designed to burnish that image in the voters' minds.

According to Vogel, the Soviets also indicated to him that they would be willing to separate the count of nuclear-armed aircraft from missiles in the arms-reduction talks--another requisite of public U.S. positions.

The primary Soviet weapon aimed at western Europe, the SS20 missile, contains three warheads, while the U.S. missiles scheduled for deployment in western Europe later this year are to be armed with only one warhead apiece.

Until now, the Soviets have indicated willingness to reduce the number of SS20s to match the total of British and French intermediate missiles. Not all of the 162 British-French missiles have multiple warheads, so the Soviet reference to a balance of warheads could mean a new flexibility--perhaps including acceptance of some U.S. Pershing II and cruise missiles in Europe as now planned by NATO. The public Soviet position has been to oppose that deployment absolutely.

During 2 1/2 hours of talks with the new Soviet leader, Vogel said, Andropov told him the Soviets were prepared not only to scrap some of their missiles but also remove others to points so far east that they could not strike West Germany or other West European countries.

Vogel added, however, that the number of missiles to be destroyed and whether these would include the modern SS20 and not older weapons systems "will have to be issues of negotiation." He also described the Soviets as willing to calculate separately the balance of nuclear missiles and that of nuclear-equipped aircraft, as the West has long demanded.

Vogel flew to Paris this morning, to inform French President Francois Mitterrand about his trips to Washington and Moscow over the past week, then returned for his press conference.

Vogel said the Soviet leadership realized that French and British nuclear forces could not be included in negotiations with the United States in Geneva, but insisted that these arsenals be counted in any overall assessment of the nuclear balance in Europe.

Mitterrand stressed in response, Vogel said, that France could not reduce its nuclear military component because it was required for "national integrity," but that Paris would welcome a U.S.-Soviet agreement in Geneva.

Rejecting charges from Bonn's conservative government that the Social Democrats were undercutting the West's negotiating position, Vogel contended that his party sought an accord that would "radically reduce" the Soviet medium-range missiles and cancel deployment of the new U.S. missiles.

"We don't want any missiles pointing at us from the east nor do we want missiles on our soil posing a threat to the Soviets," he said.

Vogel said that President Reagan's "zero solution," in which no Soviet nor American land-based nuclear missiles would be allowed in Europe, was an ideal goal but not feasible.

"Experience shows that negotiations rarely reach a final result that is identical with the starting position of one of the parties," he said.

Vogel remarked that he was perhaps the last foreign visitor to discuss the Euromissile negotiations in Washington with Eugene Rostow before he was compelled to resign as director of the Arms Control and Disarmament Agency.

Vogel said he did not want to get embroiled in personnel matters, but he was comforted by the fact that "the views of Paul Nitze," the U.S. negotiator on intermediate nuclear forces, "were on the same line as Rostow's" and that this would not be affected by Rostow's departure.

But Social Democratic arms expert Egon Bahr, who accompanied Vogel on his trips to Washington and Moscow, said he gained an impression of serious differences within the Reagan administration on what course to pursue in the Geneva talks and found the resignation of Rostow "not particularly reassuring in this context."

Here in Bonn, the Free Democrats' party leader, Foreign Minister Hans-Dietrich Genscher, has tried to lure new support for his beleaguered party by urging an "interim solution" that calls for reduced levels of Soviet and U.S. missiles by 1984 while negotiations continue toward the goal of precluding both sides' missile arsenals in Europe.

That approach opened a breach with the senior ruling party, the Christian Democrats, who favor sticking with Washington's zero option as a negotiating tactic.