A 61-year-old Charles County woman has died of Legionnaires' disease, and the illness is suspected as the cause of the death of a 44-year-old woman and an outbreak of pneumonia-like symptoms in 42 other persons in the county, Maryland health officials said yesterday.

State health officials issued a warning yesterday to Charles County residents, especially those over the age of 30, to seek immediate medical attention if they are experiencing chills, fevers of 102 to 105 degrees, a dry cough, stomach pains or other flu-like symptoms. Men are twice as likely to get the disease as women, according to Dr. Feng-Ling Lin, a state Department of Health and Mental Hygiene epidemiologist.

The health officials refused to identify either the 61-year-old victim, who died Thursday, or the 44-year-old, who died last Tuesday.

The disease, which if untreated has a mortality rate as high as 30 percent, strikes an estimated 25,000 persons a year. It is carried in water by a bacterium called legionella pneumophila, which can infect persons who inhale the contaminated water vapors often through air conditioning systems or shower heads. Proper treatment with antibiotics lowers the mortality rate to 5 percent, health officials said.

Yesterday, officials said they have not yet isolated any common source of the disease in the county, but were continuing to investigate.

Many of the Charles County patients are retired, disabled or unemployed individuals who stay at home, according to Dr. John G. Bartlett, chief of infectious disease at Johns Hopkins University Hospital, who went to Charles County on Saturday to consult with local health officials.

"It's a little bit mystic to me that almost all of this has happened in the last three weeks, when it's been miserably hot and people are turning on their air conditioners for the first time. Maybe they'll find a common building or restaurant, but it's a pretty heterogeneous group . . . of people over 30," Bartlett said.

"It is not spread through person-to-person contact so it doesn't threaten family members or personnel in hospitals. There's no evidence that drinking water is involved," said Mary Haag, director of community relations for Physicians Memorial Hospital in La Plata, where 17 patients suspected of having the disease are being treated with antibiotics.

Thirteen others have been discharged from Memorial Hospital, one patient was transferred to Georgetown University Hospital and 11 other county residents are being treated by their family doctors, Haag said.

The relatively rare disease received national attention in 1976 when 182 people attending an American Legion convention at the Bellevue Stratford Hotel in Philadelphia became ill. Twenty-six of them died.

Health officials have since identified at least 30 outbreaks of the disease, Bartlett said, including one at St. Elizabeths Hospital in 1965 in which 16 of 94 victims died. The disease had not been identified at that time.

In many of those epidemics, the disease was spread through air conditioning systems in hospitals or hotels. But Bartlett said there have also been regional outbreaks, such as one in the late 1970s in Burlington, Vt., and another in Nottingham, England.

Maryland, with about a dozen cases reported each year, has a low incidence of the disease, Bartlett said.

State health officials said they were first alarmed by doctors' reports of four times the average number of pneumonia cases in May scattered throughout the county, which has a population of about 16,000. Neighboring counties have not reported similar outbreaks, officials said.

"Pneumonia is any infection of the lung; Legionnaires' disease is an infection of the lung caused by legionella," Bartlett said in describing the difference.