Members of the Teamsters union delayed the departure of a Soviet jetliner from Dulles International Airport for nearly two hours last night, refusing to load cargo on the plane as a "sign of support" for President Carter's stand on the Soviet invasion of Afghanistan.

Pan American Airways ticket agents, members of Teamsters Local 732, also refused to process passengers, including 15 members of an American boxing team, bound for Moscow on the plane's scheduled 6 p.m. flight.

Airport officials said 42 passengers were transported to the four-engine aircraft in a mobile lounge at 7:10 p.m. after Soviet Embassy personnel, using an embassy truck, loaded their bags aboard. The plane took off at 7:50 p.m.

The departure followed hours of confusion as Soviet and American officials and union leaders argued over the flight.

Soviet personnel said they had set up a temporaty ticket counter in the airport lobby at one point, only to have it removed by Americans they identified as Teamsters members. "It's like a kindergarten game," said one angry Soviet official.

Faced with the refusal of union members to remove cargo from the plane, a group of Soviets managed to umload about 4,000 pounds of cargo, which was taken to the airport's customs area.

Teamsters officials said the cargo will not be allowed to leave the field.

Two of a group of about 20 Soviets clustered outside the terminal building told a reporter that the refusal to release the cargo, which includes goods for the Soviet Embassy here, violtes international agreements.

One of the Soviets, who refused to give his name, said the action is "very close" to the Iranians" disregard for international law in the takeover of the U.S. Embassy in Tehran.

As the delay of the plane's takeoff lengthened, William Ferchak, an international Teamsters representative, said, "Nobody will handle anything on the Russian plane. If Pan Am does anything right now (to help the Aeroflot passengers), I'll pull the people off the job."

Ferchak said that Pan Am, under an agreement with Aeroflot, handles ticketing and baggage processing for Aeroflot flights at Dulles and at New York Kennedy Airport.

Ferchak said Pan Am telephone reservation clerks also were refusing to take reservations for Aeroflot flights.

Ferchak was interviewed as he emerged from a meeting with representatives of Pan Am, Aeroflot and the U.S. State Department who were trying to resolve the situation.

Earlier yesterday, airport employes had refused to unload the cargo from the Soviet Ilyushin 62M shortly after its arrival from Moscow. They did remove baggage belonging to 32 incoming passengers to the terminal building.

Members of the machinists union employed by the Allied Aviation Fueling Co. fueled the plane after its arrival yesterday afternoon, according to a union spokesman.

Airline employes at Kennedy Airport caused delays in Aeroflot flights last Sunday. Ferchak said that the Russians, anticipating a work stoppage at Dulles, had canceled last week's regularly scheduled flight to Washington. a

Yesterday's flight was the first to land here since the Teamsters protest began.

"We feel that patriotism has been absent from the scene for a long time," Ferchak said. "We are frustrated about what's happening in Aghanistan and Iran. This is a way to vent that frustration."

Airport manager Dexter Davis said the Soviets apparently brought "a lot of their own people over, just in case something like this happened. I saw a lot of strange people hanging around the airplane.

Ferchak criticized the boxing team's trip on a Russian airline as "a very selfish and unaware act for them to do."

The American Athletic Union (AAU) team is scheduled to appear in Moscow as part of an exchange that has been going on with the Russians for about 10 years, according to the trip's organizer, retired Army Col. Dan Hall.

Alex Ramos, 19, a light middle-weight from New York City, sat looking glum last night as airline officials debated the outcome of his long-awaited trip to the Soviet Union.

"I feel a little nervous," Ramos said of the controversy. But he added, "I don't think politics should be involved in sports. Lots of athletes have been training for many years."

Hall, wearing a red, white and blue tie with an American flag pattern, said most of the $15,000 needed to pay for the trip was raised last year when a Russian team toured the United States.