Moscow — Beyond the anti-US posters, the crowds, and slogans of an officially organized Moscow ''peace demonstration'' over the weekend lies widening Kremlin concern that Western Europe will go ahead with plans to start deploying new United States missiles in December.
A ''statement'' adopted with obliging unanimity by marchers on a chilly Moscow Saturday, blasted ''plans of the US and NATO to base new nuclear rockets in Europe.'' A new pop song for the occasion wailed: ''Stop, stop, Mr. Reagan!''
Moscow seems intent on hiking efforts to prod some last-minute reversal, or at least a delay, in that deployment. But the Soviets also seem increasingly skeptical such a campaign can succeed.
A generally hard-line Soviet official did tell the Monitor Friday that, despite an unprecedently bleak statement from Kremlin chief Yuri Andropov last week, Moscow was not ''giving up'' on dealing with the Reagan administration.
He said Mr. Andropov's intent was to convey ''a genuinely serious warning . . . of the urgency of achieving the aim'' of the stymied Geneva talks on Euromissiles. ''If this voice of reason is not heeded,'' he said, Moscow would ''do what we've done for the past 40 years or so,'' and counter the West's deployments.
For some months, officials have made it clear privately that they do not feel the NATO deployments can be derailed by anti-nuke demonstrations in the West. The key, they say, must lie in Geneva.
But sources who some months back held out hope of success of the negotiations now seem increasingly skeptical.
One ray of hope is that US elections are nearing and Mr. Reagan may be more anxious for an arms accord than in the past, wrote a Soviet columnist reportedly trusted by Mr. Andropov.
Yet things have been going badly for Moscow. Elections this year have favored pro-Reagan leaders in two key NATO countries: West Germany and Britain. Ties with France have also been strained.
And no sooner had Mr. Andropov made his latest major policy statement on Euromissiles, than the Korean airliner tragedy undermined Soviet credibility in the West for at least a while, and threw Moscow on the international defensive.
Central issues in the talks are the more than 200 triple-warhead SS-20 missiles aimed at West Europe, and which weapons to count to produce a balance between the SS-20s and NATO weapons.
Moscow says any accord must keep enough SS-20s to balance the 162 missiles belonging to France and Britain. The West argues the British and French arms are inferior to the SS-20s, controlled independently, and not meant for defense of other European states. Neither side has shown any give on the issue.