The State Department, in an effort to counter Soviet claims that President Reagan used inaccurate and "absolutely fantastic" figures this week in assessing the balance of atomic striking power in Europe, yesterday released more detailed figures to support the president's claim of a 6-to-1 Soviet advantage.

The State Department's accounting is the latest round in a public war of words and statistics between Washington and Moscow, even though the two countries are still eight days from opening negotiations in Geneva on limiting or eliminating opposing missile forces in Europe.

Although this numbers battle is part of a crucial fight for public opinion in Western Europe, where the North Atlantic Treaty Organization wants to install new missiles to balance the Soviet edge if arms talks fail, it also reflects what the real fight will be about when the doors close behind the negotiators Nov. 30.

That battle will involve how many weapons are in each nation's arsenal and which should be counted in assessing the balance of intermediate- or medium-range striking power, meaning weapons that can be fired over distances of several hundred to perhaps 3,000 miles.

As Reagan proposed in his televised address Wednesday, the United States would be willing to cancel the deployment set to begin in 1983 of 572 new Pershing II and cruise missiles in Western Europe if the Soviets dismantle their 250 new SS20 missiles and 350 older SS4 and SS5 missiles already deployed.

In revealing that proposal, Reagan displayed charts showing that not only did the United States not have any comparable missiles in the field, but also that the Soviets had nearly 4,000 systems--missiles and airplanes--based in the Soviet Union or Eastern Europe and capable of carrying atomic warheads to hit Western Europe.

The United States was portrayed as having slightly more than 500, all of them aircraft.

It is these figures the Kremlin called "absolutely fantatstic."

The State Department said yesterday that the Soviets have 3,825 medium- or intermediate-range nuclear forces including, aside from the 600 SS20, SS4 and SS5 missiles, 100 SS12 or SS22 missiles, the latter being the improved version; 45 Backfire bombers, 350 older Badger and Blinder bombers; 2,700 Fencer, Flogger and Fitter jet fighter-bombers, and 30 older SSN5 submarine-based missiles.

The aircraft designations are NATO code names for the planes.

The U.S. force, State reported, amounts to 560 planes, including 164 F111 and 265 F4 fighter-bombers based in Europe, 68 Navy A6 and A7 attack planes on carriers in the Mediterranean and 63 bomber versions of the FB111 based in the United States but deployable to Europe.

The United States, as senior officials have made clear, wants initial negotiations to focus only on missile forces, not on air or naval forces.

The U.S. statistics are meant to show the Soviets as having a big edge that they should cut back.

They also are meant to warn that if Moscow insists on charging that all U.S. planes in Europe capable of reaching Soviet territory--which the Soviets call forward based systems--should be counted in the balance, the United States will insist that all Soviet planes capable of bombing Western Europe be counted.

The United States, officials said, may be prepared to discuss these forward based forces later in the talks, but only assuming success in the missile discussions. Even then, it is not clear now how this aspect would be handled.

Things look very different from Moscow's perspective.

Soviet President Leonid I. Brezhnev, who fired the first public salvo in an interview with the West German magazine Der Spiegel earlier this month, claimed that "an approximate parity" exists between NATO and the Soviet Union.

Brezhnev claimed that the United States alone had more than 700 aircraft surrounding Soviet borders and that the British had 64 missiles and 55 bombers and the French had 98 missiles and 46 bombers.

The NATO allies' total, he said, was 986. The comparable Soviet figure, he claimed, was 975.

Brezhnev noted that all these Western weapons can hit Soviet soil but that the Soviet weapons cannot reach the U.S. mainland.

He also claimed that the new SS20 missiles were meant to replace the older SS4 and SS5 missiles put there originally to counter the Western aircraft force.

Secretary of Defense Caspar W. Weinberger said Thursday that there was "no way" the United States would "negotiate away" the forces of other nations, meaning Britain and France.