A measles outbreak has infected six students at the University of Maryland in College Park, despite a massive immunization program on campus in which almost 3,000 students have been given vaccine, health officials said yesterday.

Dr. Margaret Bridwell, director of health services on campus, said two cases of the highly contagious virus have been confirmed. Four other students, she said, have come down with an illness that has been identified as measles by its symptoms but that has not yet been confirmed by blood tests.

"You've got one case, and it's serious as far as I'm concerned," Bridwell said.

"I think we have to call it an outbreak."

Mark R. Johnson, a health services specialist for the state Department of Health and Mental Hygiene, echoed Bridwell's concern. "It's a potentially dangerous situation because you can end up with very sick people and you can end up with people who, if they aren't treated, can die," he said. "We at the health department consider even a single case dangerous because there's always the potential for spread."

Symptoms of measles are high fever, cough, running nose, eye inflammation and a red rash, and complications include pneumonia, deafness, brain damage and death. Following the development of a vaccine for measles in the 1960s, the disease has become relatively rare. Now few people build up natural immunity to it, Bridwell said, so "when somebody does get it, they get it even worse."

Bridwell said that four of the cases on campus have involved electrical engineering students.

Campus officials inoculated 638 students, including more than 90 engineering students, Wednesday, and another 170 engineering students received vaccinations at a special clinic set up in an engineering building yesterday.

Almost 3,000 students at the 38,000 student campus have been vaccinated this year, and another clinic is scheduled today, Bridwell said.

Bridwell said she had "no idea" how the outbreak started. School officials, she added, have not uncovered any particular link among the victims, such as a shared class.

She said the infected students, four men and two women, range in age from 19 to 32.

Measles experts at the national Centers for Disease Control estimate that between 5 and 15 percent of young adults are not protected against measles.

College-age students are particularly susceptible, they said, because they grew up during a period when the disease was on the decline -- meaning that few contracted the disease while children and thus did not develop a natural immunity to it.

At the same time, however, many who were inoculated did not receive an effective form of the vaccine.

Measles cases have been reported at 17 college campuses across the country this year, according to Dr. Ronald Davis of the center's division of immunization. The worst outbreaks occurred at Principia College in Illinois, where 128 students came down with the virus and three died of complications from measles, and Boston University, with 110 cases.

Marilyn Berman, assistant dean of engineering at the University of Maryland, said that engineering students were "going in and dutifully getting the shots" and that one professor yesterday dismissed his class early and led students to the makeshift vaccination center.

"I got one today," she said. "It hurts."