Keely Vienne, a 20-year-old sometime student, entered the University of Maryland Hospital here recently to contract a case of traveler's diarrhea and earn $30 a day.

Vienne is one of more than 600 persons, mostly young and only marginally employed, who since 1974 have served as human guinea pigs in research projects at the University's Center for Vaccine Development. The center is the only facility of its type in the nation engaged in such research on a full-time basis with paid volunteers.

College students and dropouts, farmhands and film makers, unemployed veterans and scholars, the volunteers are exposed to such diseases as cholera, flu, and in this case, traveler's diarrhea, known variously as the Malta Dog, La Tourista, Montezuma's Revenge, Aztec Two-Step, Casablanca Crud and Delhi Belly.

The tests conducted at the center are often the first stage in human testing of a particular vaccine. Further tests are conducted on large groups of volunteers in various communities before a vaccine may be approved for general use.

The center and its procedures were developed five years ago when experimentation involving human subjects was under heavy professional and public criticism. Most critics complained that test volunteers were not true volunteers and were often unaware of what they were becoming involved in. A decade ago vaccines and drugs were generally tested on prison inmates and mentally retarded persons in institutions.

During their two weeks in the hospital isolation ward, Vienne and her 16 fellow volunteers will live a life described by center officials as similar to that in a coeducational summer camp. Their surroundings also bear some similiarity to a college dormitory.

Each of the six bedrooms has a television set and modern, wooden bunk beds rather than hospital furnishings. The day room, with its constantly droning color TV and couches designed to match the bunk beds, looks more like a college common room than anything else.

The volunteers, who dress in their usual street clothes, may play pool, do their laundry, use the ward's exercise machines, sleep and eat when they want to. The only things they have no control over are how sick they will become and their freedom to leave the unit. Once a test is begun the volunteers are committed to remaining until they are cured.

The first three days in the ward, the volunteers are not even ill. Their relaxation and socialising are interrupted only by thorough physical examinations and a two-hour psychological examination - designed to screen out people unsuited for living in close quarters and those with unsuitable motives for being in the program.

By the time the volunteers receive their disease and vaccine -either by injection or orally - they have already swallowed plastic tubes used to monitor the secretions in their stomachs. They wander about the unit with strings that are attached to those tubes dangling from their mouths.

Vienne, who sat playing Scrabble with other volunteers during a recent interview, said she entered the center "because I knew I'd only be here (in Baltimore) for a short time and, frankly, I need money . . . I've been living in New Hampshire for the last two years going to school and working part time."

Vienne, who is visiting her parents for a month, said, "Someone offered a job to me but I didn't want to take the job because I'd only be home for a month.I could have lied to him, but I didn't want to."

Kenneth Bichell, a 19-year-old Towson State College student and farm worker, saw an ad in his school paper asking for volunteers. "I needed the money and I needed a chance to get bored. I needed to get out of constantly doing something. I need a chance to collect my thoughts."

Bichell said his family "wasn't too keen on the idea at first, but when I explained the project to them, they thought it was okay."

The center began as a federally funded pilot project to see if vaccine research could be conducted in an open society concerned with the problems of informed consent and patients' rights.

Dr. Myron M. Levine, the center's director, was once involved in vaccine testing at the Maryland House of Correction at Jessup. The program was attacked by the American Civil Liberties Union and came to a halt in 1976.

The prisoners were paid $3 a day and isolated in a special prison unit. According to Alvin Bronstein, of the ACLU's National Prison Project, "the conditions in the prison were so gross that the prisoners were coerced into the program to get . . . better conditions and the money."

Levine denied that coercion was ever proved. He also said: "Looking at it from 1979, I have some qualms. Looking at it from 1970, I have no problems. I see nothing wrong with mores and ethics changing with time. What I do see is the danger of trying to judge 1970 by the ethics of 1979."

He continued: "In the late '50s and '60s, people began to recognize that people who are incarcerated can't make these decisions for themselves. What came to be accepted is that it probably isn't right to ask the parent of the mentally retarded child to use the child to test . . . vaccines."

Hence, the center here, which places advertisements in college newspapers and major dailies in the Washington-Baltimore area. One such ad last year said:

"Volunteers needed to participate in a vaccine research study at the Center of Vaccine Development, University of Maryland Medical School. Two part study:

"1/ Outpatient - month of November, two short outpatient visits a week in University Hospital for four weeks to receive vaccine (paid approximately $155 for completion).

"2/ Inpatient - 14 days (January 2 through January 16, 1979) in dormitory-like ward at University Hospital (paid approximately $350).

"For completion of both parts of the study paid approximately $500.

"Studies are part of ongoing studies of cholera vaccine at the Center for Vaccine Studies. All volunteers must be in good health and at least 18 years of age. Accepting volunteers now. For more information call . . . as soon as possible."

While the ad does not exactly explain that the volunteer in that particular study would be given cholera, that was spelled out in vivid, extensive, detail long before the volunteer was even shown, much less asked to sign, the informed consent form.

Every volunteer in any of the center's studies is put through a two-hour lecture on the study and its purpose. At the end of the lecture the volunteer is given a written test on which he or she must score between 60 and 70, depending on the study. A sample question from the cholera exam:

"When the glutaraldehyde treated cholera toxoid was tested in large-scale field trials in Bangladesh, it was found to be:

"a/ highly effective for more than one year.

"b/ minimally effective for about 8 weeks.

"c/ not effective at all."

Some of the exams, said Levine, have been flunked by some of the world's outstanding gastroenterologists. A volunteer who flunks is barred from participating in the program.

The consent form a volunteer signs before any testing begins spells out the purposes and risks of the particular test.

The form signed by Vienne and her fellow volunteers contained, among other things, the following information:

"I have been told that the bacteria I will be swallowing is a strain of E. coli known to cause diarrhea. I understand that these E. coli were obtained from patients with diarrhea in Bangladesh (strain H10407) or Viet Nam (strain B7A0.) These bacteria cause diarrhea by the effects of protein toxins (enterotoxins) made by the bacteria, which act on the lining of the small intestine and cause an increased outpouring of intestinal fluid. I understand there is a strong possibility that I may develop nausea, vomiting, fever and watery diarrhea after I swallow these bacteria. I am aware that the diarrhea may possibly be severe, resulting in the loss of so much body fluid that I will have to receive intravenous fluids (into my vein) to replace lost body fluid . . ."

Why would anyone sign such a form and subject themselves to a malady that turns dream vacations into long-remembered nightmares?

Volunteers say there are three basic reasons:

They need the money.

They know there is a doctor in the unit 24 hours a day and they will be well cared for.

And, as one volunteer put it: "I don't think I'll get it that bad." CAPTION: Picture 1, DR. MYRON M. LEVINE . . . director of center; Picture 2, Hilary Paul reads on upper bunk in her room, similar to one in college dorm.; Picture 3, Vaccine development center volunteers play Scrabble in lounge at U-Md. Hospital, Baltimore. From left are Ken Bichell, Hilary Paul, Keely Vienne and Loel Harvey. Tubes in their mouths are to monitor internal fluids. Photos by Douglas Chevalier - The Washington Post