Twenty-one Jewish college students arrested last October for protesting too near the Soviet Embassy received suspended jail terms and fines yesterday, using their trial for the same purpose as the demonstration: to focus attention on persecution of Jews in the Soviet Union.

Before D.C. Superior Court Judge Joseph Hannon pronounced the sentences of 15 days in jail and $50 fines, suspended pending appeal, he permitted six of the students to make statements.

"I know what I did was illegal, but I still feel I had to do do it," said Joyce Kammerman, a student at American University. "As a Jew, I felt it was my responsibility to help others get their rights to exercise their religion -- rights that we take for granted."

Mark Lieberson, a student at the University of Iowa, said he recalled stories of his Russian grandparents about Jewish persecution in the Soviet Union and how they "escaped from Russia . . . . But with modern technology, it's not so easy to escape today," he said.

While indicating that he was in sympathy with their motives, Hannon stressed his obligation to uphold the law. "It is not given to me to ignore this law for whatever reason," he said.

Citing the current conflicts in the Philippines and in Haiti as examples of what happens when laws are flouted, he said: "If we are going to live by the law, it is extraordinarily important that . . . judges and district attorneys and police officers enforce this law."

As the students filed out of the courtroom, their attorney, Lawrence M. Baskin, raised the question of having their convictions ultimately expunged from their records, under provisions of the Youth Rehabilitation Act of 1985.