A Soviet Foreign Ministry spokesman suggested today that a freeze on nuclear weapons proposed by President Konstantin Chernenko could include U.S. medium-range nuclear missiles recently deployed in Western Europe and presumably subsequent Soviet deployments described as Moscow's countermeasures.

Vladimir Lomeiko, the ministry's first deputy press chief, said the Soviet proposal for freezing nuclear arms would include the NATO missiles in Europe "at the level that exists now."

Briefing foreign and Soviet journalists, Lomeiko said that Moscow believes that nuclear weapons in East and West were in approximate balance now. He insisted that Moscow's demand for the withdrawal of Pershing II and cruise missiles was not a precondition for the resumption of the Geneva talks but that their withdrawal "is common sense."

Western journalists who attended the briefing said Lomeiko's remarks were ambiguous and somewhat confusing, and that it was not clear to what extent Moscow has moved from its previously announced position that the West must show readiness to "return to the situation" existing prior to the U.S. deployments before the talks on strategic and medium-range nuclear arms could be resumed.

Lomeiko insisted during the briefing that Moscow was not imposing conditions for the resumptions of these negotiations.

"If the United States sincerely wishes a breakthrough in relations then there are many routes to prove this willingness," he said. He alluded to Chernenko's interview with The Washington Post earlier this week in which the Soviet leader singled out four areas in which progress would open the way to a broad dialogue -- a nuclear arms freeze, a ban on space weapons, ratification of nuclear test treaties and renunciation of first use of nuclear arms.

"The U.S. administration has not displayed willingness to take even one single measure" advanced by Moscow, he said.

Western observers said Lomeiko's pronouncements were so ambiguous as to make it difficult to ascertain whether he was signaling a change in Soviet definitions or was merely trying to "muddy the waters" before the forthcoming debate on foreign policy between President Reagan and Democratic presidential candidate Walter F. Mondale.