The Reagan administration has sent a chilly private message on superpower relations to a senior Moscow official, Soviet and Western sources here report. Soviet officials, evidently surprised and irked by the move, say the US Embassy here later tried slightly to soften one point in the message: rejection of the idea of informal talks between Washington and Moscow.
A top embassy official is said to have told the Soviets this exclusion of so-called "back channel" contacts, an avenue popularized by former US Secretary of State Henry A. Kissinger, was meant to apply only to substantive negotiations.
Highly placed Soviet sources said the message also reiterated what they see as a heavy- handed and uncompromising public approach by Washington to overall superpower relations.
The US is said to have stressed that these ties must be based on "reciprocity and restraint" as well as on "linkage," the concept that progress on such issues as arms control would be tied to Washington's evaluation of Soviet behavior in other areas.
US Embassy officials would neither confirm nor deny the reports on the message. Other Western diplomats confirmed the general lines of the story but offered no details.
The message was reportedly delivered orally from a prepared text by acting US Ambassador Jack Matlock to Georgi Arbatov, the Kremlin's foremost brain truster on American affairs, after Mr. Arbatov returned from a visit to the US spring.
A senior official quoted the note as saying, on the "back-channel" issue, that there were ample official avenues of communication and that new "official or semiofficial" links were neither desirable or necessary.
What prompted the message remains unclear.
A recent Washington Post article quoted a US businessman who visited here as having said Mr. Arbatov suggested reviving "backchannel" contacts during a conversation with him. Mr. Arbatov offered to serve as one such conduit, the report said.
In a July 28 interview with the Monitor, Mr. Arbatov denied this, saying he had merely repeated what have become frequent Soviet calls, public and private, for the superpowers generally to use any and all possible means to revitalize their dialogue.
He argued that the Reagan administration was systematically "destroying the infrastructure of confidence" between the two sides, and that this was creating a "dangerous" situation.
He questioned the logic of large-scale increases in US military outlay, saying this would merely reinvigorate the arms race without bringing other areas of superpower conflict any closer to resolution.
"What is needed is contacts on all levels," he stated.
Mr. Arbatov refused to comment on the reports that he had received a message from the Americans, saying to do so would be "improper."
Other Soviet officials, speaking privately, were less reticent.
They quoted US diplomats as presenting the message as a rejoinder to various criticisms of Reagan administration policy by Mr. Arbatov.
Mr. Arbatov's visit to the US earlier in the year figured in something of a superpower shouting match, when the Americans denied him a visa extension to appear on a television discussion program.
Senior Soviet officials, interviewed over recent days, seem still to hold out hope for eventually thawed relations with Mr. Reagan.
But the tone is unanimously far more pessimistic than it was months, or even weeks, ago.
One official, alluding to the US message to Mr. Arbatov as one disturbing sign, said it seemed increasingly clear that Washington's public "anti-Sovietism" was not just a product of rhetoric or "inexperience," as some Soviet analysts had been assuming.
He said it seemed likely that "we are in for several very hard years" in superpower relations, adding, "I only hope that we don't have to cope with some really serious international crisis" against such a background.