Moscow — The Soviet Union is showing signs of restraint toward unrest in Latin America , a concession to President Reagan that jibes nicely with its own long-term aims in the region.
Diplomats here stress there is still no firm indication the Kremlin is going as far as Mr. Reagan would like in abandoning alleged support for communist arms shipments to El Salvador.
That, presumably, would mean some form of noninterference pledge, coupled with a directive to East Europe, Cuba, and other Soviet allies to fall into line.
The official Soviet news media also continue to hint at US military intervention in the region.
The press has also been highlighting what is painted as crude US pressure on Nicaragua, with the apparent hope that the revolutionary regime there, still avowedly leery of alliance with either superpower, will move closer to Moscow.
Indeed, some diplomats here argue that a more muscular US stance -- whether in pressuring a left-oriented country like Nicaragua, or in backing El Salvador against leftist violence -- could ultimately benefit the Soviets.
Such US action could conceivably strain the Western alliance, divert attention from the Soviets' own backyard crisis in Poland, or prompt a backlash against Washington in Latin America.
Still, the bottom line in recent Kremlin policy toward Latin America appears to be: no potential Soviet windfall there is worth endangering an eventual improvement in relations with Washington, with the eventual improvement in or with economically important Latin American states like Argentina, Mexico, venezuela, and Brazil.
This equation came across clearly at the recent Soviet Communist Party Congress here. To the surprise of diplomats, Soviet President Leonid Brezhnev omitted mention of El Salvador in his marathon keynote review of Soviet domestic and foreign policy.
No Salvadoran delegation was listed on the roll of foreign communists and leftists attendthe congress. Allied Cuba got only a cursory note in Mr. Brezhnev's speech
But friendlier treatment was given to distinctly noncommunist states like Mexico and Venezuela (which have oil) and Argentina (whose increased grain sales to the USSR have taken some sting out of Washington's grain embargo against the Soviets).
"We are pleased to note the expansion of the Soviet Union's mutually beneficial ties with Latin American countries," Brezhnev said.
Days later, the president of the Argentinian grain board was in Moscow for talks that reportedly included the issue of further shipments to the Soviet Union.
Cuban communist leader Fidel Castro, naturally, got a warm welcome at the congress.Mr. Brezhnev gave him a bear hug. He was the first foreign communist to address the assembly, and the first to huddle with the Soviet President in the Kremlin.
But the Soviet communique on the meeting struck most diplomats as restrained, by past standards, in its cheerleading for the Cubans.
In the toned-down echo of Mr. Castro's fiery speech to the congress, the statement said US "imperialists" were "launching another anti-Cuban campaign."
But Mr. Brezhnev's bid for repaired relations with the West also seemed to sound through in the operative phrase of the communique:
"The USSR as before, is siding with socialist Cuba and expressing full support of its principled policy of peace and friendship among peoples."