President Reagan has instructed his chief arms negotiator, Paul Nitze, to do everything he can to find a crack or an opening for compromise with the Soviets in the Euromissile talks in Geneva.
But the Soviet Union is being even more rigid than earlier in the talks, and Mr. Nitze has been unable to find any such crack.
That is the assessment of a senior United States official who attended the recent West German-American conference of the Friedrich Ebert Foundation here in Bonn.
The official said that Nitze has offered the Soviet Union any equal numbers between zero and 450 for nuclear missile warheads on both NATO and Warsaw Pact land-based intermediate-range forces (INF). The official added that the Soviet Union has not responded with any number.
In fact, he indicated, the Soviets have hardened their position. The Soviet offer this spring to move to warheads rather than missiles as the counting unit has turned out not to compensate for the three-warhead Soviet SS-20 as against NATO's planned single-warhead cruise and Pershing II missiles.
Instead, it is clear from the Soviet amendment to its draft treaty proposed in the current round of negotiations that this move is intended to justify Soviet retention of all its already deployed SS-20s - and even permit their increase - by counting them against the planned increase in British and French warheads under their modernization programs for the 1980s.
The current Soviet position, like all previous official Soviet proposals, it was noted, would thus leave in place all of the more than 360 SS-20s deployed since 1977. It would at the same time not only bar any US INF missiles from the European continent, but also eliminate all existing US dual-capable (nuclear and conventional) aircraft from Europe and from adjacent Mediterranean and Atlantic waters.
The American official, along with a second senior American official at the Ebert conference, further stated that it was Moscow, not Washington, that summarily rejected last summer's ''walk in the woods'' exploratory package. The two US officials categorically denied published reports attributing the rejection to the US.
The first exchange of paper at Geneva after last year's summer recess, they said, involved the handing over by Soviet negotiator Yuli Kvitsinsky of his new instructions. These rejected on every count the tentative package initiated in June 1982 by Mr. Nitze and Mr. Kvitsinsky.
Nitze's instructions, by contrast, were to keep the channels open, and to say that although Washington had problems with the package's ban on Pershing IIs and the ceiling figure for Soviet SS-20s in the Far East, it wanted to discuss the issues further.
So far as is known, the Ebert conference provided the first semipublic description of the current state of the INF arms control negotiations by high US officials. Curiously, it went virtually unreported in the German press.
The ''walk in the woods,'' besides barring NATO's deployment of Pershing II ballistic missiles and limiting SS-20s in the Far East to 90, would have limited Soviet European SS-20s and new NATO cruise missiles to 75 launchers each, with 225 SS-20 warheads and 300 cruise warheads. It would have exempted French and British INF missiles from the Euromissile balance, as well as dual-capable nuclear and conventional aircraft of both East and West.
There has been considerable interest across the political spectrum in West Germany in reviving the walk in the woods - with Washington rather than Moscow cast as the side that is reluctant to do so. When asked if refloating the package would cause the US any problems, the second US official replied:
1. It would be inconsistent with the US insistence on Soviet-American global equality in INF warheads.
2. The Soviets would reject it.
The Soviet rejection of the walk in the woods reportedly came when the package was not presented directly to Soviet President Leonid Brezhnev in the period shortly before his death, but went through the regular committee process, in which the top Soviet military command plays a decisive role.
That process resulted in a firm ''nyet,'' with insistence that American ''forward based'' aircraft and British and French missiles all be included in the INF balance.
On the American reaction to the walk in the woods, a number of sources in Washington and Western Europe doubted whether the American expression of continued interest was anything more than a formal, cosmetic covering for a basic rejection of the walk-in-the-woods compromise.
They said that the US military had killed the concept in Washington as thoroughly as the Soviet military had killed the idea in Moscow - for reasons that had far more to do with service infighting than with real security needs.
The sources said that the chairman of the Joint Chiefs of Staff, Gen. John W. Vessey Jr., initially found nothing objectionable in waiving deployment of Pershing IIs altogether as part of a deal. But his own parent service, the Army, complained bitterly that if it lost its budget for the Pershing, this would unravel the entire Army budget, to the advantage especially of the rival Navy.
The Army command is therefore said to have forced General Vessey to oppose forfeiture of the Pershing II in the second Washington meeting to consider the walk in the woods, held a month after the initial consideration. Since that meeting this opposition has been a firm feature of the American position.