Undated (AP) _ Health officials focused on air conditioners as the sources of two outbreaks of Legionnaires' disease that killed at least four people in California and Wisconsin.

''We think we have a problem, but not an epidemic,'' said Dr. Ralph Jung, acting medical director of the 212-bed City of Hope National Medical Center, a private research hospital in Duarte, Calif., that gives free care to terminally ill people.

The disease was diagnosed in six of the hospital's cancer patients, who are exceptionally vulnerable because of their low immunity. Three died, while one was in critical condition Thursday and two were in stable condition.

In Sheboygan, Wis., health officials still could not say what was the source of Legionnaires' disease that killed at least one person and perhaps as many as four others.

Wisconsin investigators took samples of water from air conditioners, industrial cooling towers and even puddles in vacant lots on Thursday in a 15- square-block area containing most of the homes of 28 people stricken since Aug. 10 with pneumonia-like sickness.

Factories and other businesses were then told to clean the equipment with chlorine.

Five of the 28 people stricken have died. Lab tests confirmed that three of the 28 had Legionnaires' disease, including one of those who died. Thirteen people were still hospitalized Thursday, none in critical condition.

''We have an outbreak of Legionnaires' disease, said state epidemologist Jeffrey Davis.

Of the three City of Hope patients who died between March and June, Jung said: ''We don't know if they died from Legionnaires' disease, but they died with it.''

Thirty-five people have been moved from the bone marrow transplant and cancer wards to other areas of the hospital.

The Los Angeles County Health Department is analyzing water specimens from all the hospital's air conditioning units, and plans to decontaminate them next week.

''We're looking at all the usual and known sources of contamination, and the cooling system is a prime suspect now,'' said Dr. Peter Kerndt, a Los Angeles representative of the federal Centers for Disease Control.

He theorized the hospital's cooling system became contaminated when nearby construction stirred up dust, delivering bacteria into the air conditioning.

The disease was discovered in 1976, when 29 people died after contracting it at an American Legion convention in Philadelphia.

The illness is not transmitted from person to person. Its symptoms include pneumonia or other respiratory disorders, fever, chills, dry cough, vomiting, stomach pain, loss of appetite, diarrhea, muscle aches and headaches.