For the U.S. Public Health Service it was a fairly routine case: an unusual accumulation of water; reports of unexplained illnesses, and a decision to evacuate the place as a health precaution.

What makes this case a bit out of the ordinary is the scene of the suspected health hazard, a federal building in the heart of Washington, and the victims of the unexplained illness, an undetermined number of Public Health Service employes.

Shirley Barth, a spokesman for the health service, said yesterday the date hasn't been set for the move of 84 employes from Corridor B on the seventh floor of the Hubert Humphrey Building. But she said a move was necessary "because there are unhealthy conditions. . . certainly unpleasant conditions" in Corridor B.

The problem, Barth said, appears to be caused by water leaking from the cafeteria kitchen area, which is on the eighth floor directly above the offices for health promotion, planning and evaluation, public affairs and adolescent pregnancy problems.

The water--specifically the amoeba found in some samples--is suspected to be the cause of a rash of illnesses ranging from severe headaches to nausea that health service employes have experienced within the last year.

Dr. George Hardy, who works for the Centers for Disease Control and has an office in Corridor B, said the symptoms have included fevers, chills, muscle aches and nausea. "It starts out feeling like the flu," said Hardy, who experienced some of those symptoms himself before moving to a new desk..

According to a review of the problem by the National Institute for Occupational Safety and Health (NIOSH), "there is an illness on corridor 7B . . . which fits the clinical description of subacute infiltrative lung disease (hypersensitivity pneumonitis or humidifier fever)."

Dr. Michael J. Hodgson and Dr. Philip R. Morey, who conducted the review, recommended that the Corridor 7B carpeting--which had been soaked by the leaking and which therefore "could harbor micro-organisms"--be discarded and the floor scrubbed with bleach before replacement carpeting was installed. They also recommended that ceiling panels be cleaned and all wall partitions and upholstered furniture be vacuumed.

The leaks are nothing new for workers in Corridor 7B, however. Barth said they became a problem within a year after the Public Health Service employes moved into the Humphrey Building in October 1976. Repeated efforts to repair the leaks have failed, she said.

Parts of Corridor B already have been emptied of desks, chairs and files. The carpeting has been removed. Some ceiling tiles are missing while other tiles bear water stains.

Some workers have been moving around for months in search of a dry place to spread their papers. "I sat next to a drip for six or seven months," Barth said.

About half the 84 employes will move to another part of the Humphrey building; the rest will move into another building a few blocks away. There is no plan for them to return.