For voyagers wondering what shots or pills they need to face the health hazards of exotic ports-of-call, Washington has a wealth of medical resources.

The Traveler's Medical Service of Washington is opening this month at 916 19th St. NW (466-8109). It's the long-planned project of Dr. Martin S. Wolfe, an expert in tropical diseases who acts as medical consultant to the World Bank, the Peace Corps and the State Department.

Wolfe is opening the service with two other doctors, Michael A. Newman and Devra C. Marcus, in order to make more widely available the information he has been providing to special groups for years. It includes advising travelers and their physicians on disease protection, treating parasites and other illness in those who have recently returned, and taking care of foreign visitors who fall ill while they are here.

The service will be open from 4 to 6 on weekday afternoons. A nurse trained in international medicine will administer any needed immunizations and answer questions such as how to protect against malaria or travelers' diarrhea. aShe will do all routine counseling, but Wolfe said he and his colleagues will see any patients who have special medical problems.

They will also provide written advice for travelers, and -- for those traveling with a chronic illness -- referrals to qualified doctors anywhere in the world.

Appointments will be necessary, but Wolfe said he expects the service will be able to provide last-minute assistance for those who are embarking on short notice. Immunizations will cost $8 each (except yellow fever, which will cost $10) and counseling will cost $20 for a 15- to 30-minute session.

The Traveler's Medical Center is not the only such clinic in the Washington area. Georgetown University has been running an International Health Clinic for eight years, staffed by a nurse-practicioner with a public health physican to provide backup. Located on the third floor of the Georgetown Medical School building (adjacent to Georgetown Hospital), it is open Monday from 9 a.m. to noon, Wednesday from 2 to 5, and Friday from 11 to 2 (625-7379). Georgetown plans to expand the clinic's hours and move it to the hospital soon. Immunizations cost between $8 and $15 each, and counseling is free. The Georgetown clinic is not currently treating illness in returning travelers or providing referrals to doctors abroad.

George Washington University has also opened a traveler's clinic this month, at 2150 Pennsylvania Ave. NW (676-4716). Open Wednesday and Friday mornings from 9 to 12, it is staffed by infectious-disease doctors Carmelita Tuazon and Gary Simon. Immunizations cost $10 to $12, pre-travel counseling $20 and post-travel counseling $10. Drs. Tuazon and Simon can also help with referrals to doctors abroad, provide physical exams and treat illnesses acquired during the trip.

Such clinics are not designed to replace a patient's family doctor. But Wolfe said that despite travel information provided by local health departments and the Federal Center for Disease Control, some doctors do not feel comfortable advising on precautions for travel to tropical countries, or treating exotic illnesses brought home from abroad. He believes his service will be filling a void here.

Up-to-date immunization rules for individual countries are available on tape by calling a health department number, 973-9714. But Wolfe said deciding whether to have some immunizations, such as cholera or typhoid, is not always easy. These shots have side effects, and do not provide total protection. He said balancing the risks and benefits requires thorough familiarity with the diseases present in each country to be visited.