The University of the District of Columbia has suspended 1,200 of its 14,000 students and placed 1,700 more on probation in the second phase of enforcing a policy that UDC president Benjamin Alexander said is designed to increase the value of a degree from the school.

Alexander said the strict suspension and probation policy is "letting (students) know that at UDC when you do graduate, your degree will mean a great deal."

In the outside world, he said, "they'll be able to compete."

The administration of UDC, Washington's only city-supported university, "is not happy to suspend students or put students on probation, but it is something we must do if we are going to strive toward being the flagship institution for the District of Columbia," Alexander said.

Under a policy adopted in 1979 by the university's trustees, but enforced for the first time at the start of the 1982 fall semester, the school is required to place on academic probation any student whose cumulative average is less than 2.0. That average Alexander said, is equivalent to a C.

The policy calls for suspension of those who fail to achieve a 2.0 average after completing three semesters or 30 credit hours at UDC.

Alexander said the latest round of probations and suspensions was based on grades received in the just-completed fall semester. The students involved have been notified by letter of the university's action.

Students on probation must take a reduced course load of fewer than 12 credit hours in order to register for the new semester that begins Jan. 17, Alexander said. Those suspended must leave the university for one semester, but may return.

Alexander said that remedial courses are offered to those who have been suspended, and that failure to enforce probations and suspensions for those with low grades would be a disservice to the 80 per-cent of the students who he said he particularly wanted to praise for "doing a superb job."

UDC, which has an open admissions policy, has been criticized in the past for academic standards described as loose.

"There has been a perception in the past," Alexander said in an interview last night, "that UDC is not a good school . . . . UDC is a good school."

In August, a few days after Alexander, formerly the president of Chicago State University, arrived at UDC, 880 students were suspended and 1,700 more were placed on probation in an action marking the first enforcement of the trustees' previously adopted policy.

The August figures amounted to about 18 percent of the university's enrollment. Noting that the current figure is about 21 percent of enrollment, Alexander said he could not immediately explain the increase. But, he added, in coming semesters, "it's going to decrease."

After the first suspensions, he said,"few people thought this would happen again." Now, he said, "word is around" among students that "we are going to have to shape up now."

UDC, Alexander said in elaborating on the philosophy behind the enforcement policy, "has open admissions, but not open graduations."

The message of the suspensions, he said, is: "You must compete . . . You can become anything . . . you wish with a good academic record."