A group of 81 students, members of the Iranian national navy studying at Norwich University in Vermont, returned to Iran last night because President Carter ordered all Iranian government officials and military personnel to leave the country by today.

Officials at Harvard, Boston University, Northeastern University and the Massachusetts Institute of Technology said yesterday they do not believe the order, announced Monday, will affect any of their students. Edward Gill, a spokesman for the Boston office of the Immigration and Naturalization Service, said it is "highly unlikely" that there are any Iranian students in the Boston area with military or diplomatic status.

George Lara, Vermont district director of the U.S. Immigration and Naturalization Service, said yesterday the break in U.S. Iranian diplomatic relations will have no immediate effect on civilian Iranians studying in the United States. He added, however, that future requests for "extensions of stay"--renewal of the forms that grant international students permission to remain in this country--may be denied.

"The overriding factor in the decision to deport these students was their status as official representatives of the Iranian government," Lara said.

A spokesman for the Immigration Service in Washington said that most civilian Iranian students in this country would be unaffected by the order because they have permission to remain here "for the duration of their status as students."

Some students, however, are granted permission to stay on an annual basis, which must be renewed upon expiration. No decision has yet been made about how such students will be treated when their permission expires.

In addition, the Immigration Service has proposed abolishing the "duration of status" designation. If that happens, Iranians and other foreign students would have to reapply for permission to stay for a fixed period of time, usually 12 months.