Raising his plastic cup of Moskovskaya vodka at a potluck supper in Washington Grove Tuesday night, an official of Moscow's Communist Youth League toasted a crowd of 150 Montgomery County suburbanites:

"During our day downtown which was quite busy," said Vladimir Popov, "we had only one dream: to come back here."

As they finished up a four-day Washington tour, only their accents seemed to distinguish Popov and 24 other members of a visiting Soviet delegation from the locals who hosted them in a setting seemingly lifted from a Norman Rockwell painting.

For the third time in five years, Soviet visitors stayed in the homes of Washington Grove's affluent families, making the hour-long trip downtown by bus from the picturesque town of 650 that covers three-tenths of a square mile.

The group was visiting here at the invitation of the Forum for U.S.-Soviet Dialogue, a private, nonprofit organization working for the past 12 years with the Soviet's Committee of Youth Organizations.

For the most part, the visit had all the predictability of most exercises in U.S.-Soviet detente. After a serious round of discussions last week in New England on disarmament and trade, the delegation arrived here and met with Chief Justice Warren Burger at the Supreme Court and visited Sen. Edward Kennedy (D-Mass.).

Between tours of the Lincoln and Jefferson memorials, a stop at Chairman Stephen J. Solarz's (D.-N.Y.) House subcommittee hearing on "the Soviet Challenge in Asia," a whirlwind schedule of four area think tanks, and lunch at Ruby's Restaurant in Chinatown, the Russians had little spare time.

Still, Sergi Semivolos, staff member of the Communist Party of the Soviet Union Central Committee, planned to buy computer toys for his daughter and a rocket for himself before heading back to Moscow. And Vladimir Baranovsky, a researcher with the Institute of World Economy in Moscow, hoped to shop for a radio-operated toy car for his 4-year-old son.

"Whenever they had free time they went to shopping malls and factory outlets. The women bought clothing and the men bought stereos and huge radios. I don't know how they're going to carry it all home," said Carol O'Rourke of Amherst, N.H., secretary of the Forum.

Besides bargain hunting, the clear favorite extracurricular activity was moonlight swimming in Washington Grove's lake, where the vodka was traded for Pabst Blue Ribbon beer. However, two visitors reportedly opted out of swimming to watch go-go dancing in Baltimore.

At the potluck supper Tuesday, the vodka was 80 proof and the idealism nearly as strong. Music maintained the balance of power. First, the Frankonis Brothers sang in Russian, Spanish and Italian.

Next, Washington street musician Bob Devlin, a one-man band of percussion, guitar and vocals, brought both nationalities to their feet with their hands linked, swaying in a circle, singing "We Shall Overcome." Devlin encouraged the group, shouting, "Comrades!"

Only a minor disturbance spoiled the otherwise enthusiastic diplomatic exchange. From the steps of McCathran Hall, where the buffet was spread, a young man claiming to represent "the American truth squad" shouted to the gathering that the Soviets were "all KGB agents."

A panicked hostess began singing "We Shall Overcome" in an attempt to drown him out. Greg Fess, an attorney at the Department of Energy and a forum board member, rushed the man out of earshot.

And then four days of toasts resumed.