The trip to the Soviet Union as a leader of a delegation of Maryland high school students offered Montgomery County teacher Alla Sonsev a rare opportunity. She would return to her native land and visit her relatives in Leningrad.

But yesterday, just six days before Sonsev was to depart with 30 students and two other teachers as part of a national student exchange, Sonsev received word that she cannot go because the Soviets have not granted her a visa.

The 35-year-old teacher of Russian at Gaithersburg High School and Seneca Valley High School in Germantown, who emigrated from the Soviet Union in 1978, could not contain her anger and disappointment. She said the incident calls into question whether the Soviets are genuinely committed to their new policy of glasnost, or openness.

"This shows nothing has changed in my country," Sonsev said. "The basic principles of socialism have not changed at all . . . . This shows that they are afraid of people who left the country and want to come back."

Of the 90 teachers who are chaperoning more than 900 students from 38 states on a 22-day tour of the Soviet Union, all visa applications were approved -- except those of Sonsev and another Soviet-born teacher from Louisville, according to officials of the exchange program.

"They don't want me there because I would be a censorship to them," said Sonsev, a naturalized American who lives in Germantown. She is married to a Russian-born mechanical engineer and has two children, ages 10 and 12.

"They would be trying to make a good impression on the students and tell them how good the system is and how well it works. But to have someone who lived there so long who would criticize or would explain better what is right and what is wrong . . . it would be a bone in their throat."

The organizers of the exchange program, called "The Initiative for Understanding: The American-Soviet Youth Exchange Program," said they are not certain why the visas for Sonsev and the other teacher have not come through.

"I have a feeling it's more a matter of not getting {the visa requests} in early than any conscious thing on the part of the Soviets," said Norman Swanson, an official with People to People International, the private umbrella group that is organizing the exchange program.

"I don't think there's any intentional desire to hold {the visas} up, because they know the publicity they get for doing those kinds of things and there's no benefit to them," he said.

Paul Chapin, deputy director of The Initiative for Understanding, based in Spokane, Wash., said program officials will discuss the situation with Soviet officials at the Soviet Embassy in San Francisco tomorrow. "We are disappointed and we'd like to see this clarified if we could," Chapin said.

Soviet officials in San Francisco and in Washington did not return repeated calls from The Washington Post.

The student exchange program with the Soviet Union is one of many programs that have resulted from the 1985 Geneva summit between President Reagan and Soviet leader Mikhail Gorbachev when they "endorsed a new broad-based people-to-people initiative to expand direct contact between citizens of both countries," said Nancy Starr, a spokeswoman for the department in the U.S. Information Agency that oversees the exchange initiative.

William Clark, director of academic skills for the Montgomery County public schools, who selected Sonsev, said the Soviets "probably didn't want someone translating what the kids saw."

Sonsev said the Soviets' refusal to let her take the trip will have an unintended impact on the students. "My own students will question, 'Why can't Mrs. so-and-so go?' and how can they believe anything the Soviets tell them?" she said.