The Soviet Union's effusive praise for Austrian President-elect Kurt Waldheim following his victory yesterday marked an effort to shore up good relations with neutralist Austria and capitalize on strains in U.S.-Austrian ties prompted by probes into Waldheim's World War II activities, western diplomats said today.

Breaking a studied silence maintained throughout the controversy that surrounded his election, the official news agency Tass last night coupled praise of Waldheim's two terms as U.N. secretary general with harsh attacks on the Reagan administration and "Zionist circles."

At the United Nations, Tass said, Waldheim had fought for peace and security, to curb the arms race and for implementing disarmament steps.

"The U.S. administration and Zionist circles resorted to a flagrant interference in the preelection struggle and launched a campaign of personal attacks against Waldheim in an attempt to influence the outcome. . . ," Tass said.

Dismissing charges widely reported in the American press that Waldheim had participated with the Nazis in "punitive operations" during the war, Tass said, "It is now becoming increasingly clear that the true causes of the hostile campaign are not connected with his past." It added, "The accusations originate from those who shelter thousands of Nazi war criminals in the United States. . . ."

One western diplomat said today, "It is the Kremlin's way of currying favor with one of the world's most important neutral countries and exciting tensions between Austria and the U.S."

Moscow clashed with Washington over Austria earlier this year when the new American ambassador in Vienna suggested that Austria buy U.S. missiles.

Austria's 1955 treaty with the World War II occupying powers bars acquisition of missiles.

The Soviet Union, according to analysts here, is eager to protect its economic as well as political interests with the Austrian government. Moscow is a strong trading partner of Vienna.

During Waldheim's two terms at the United Nations, the Soviet Union and its allies "gained clout," in the world body, western diplomats said here.