State and Charles County health officials today began inspecting the homes of more than 40 persons in the Southern Maryland county who may have Legionnaires' disease and scrutinized hundreds of pages of information from those patients in a search for a source of the illness.

State health officials have confirmed that a 61-year-old woman died last week from the disease, a type of pneumonia that is caused by bacteria. Another woman's death last week is suspected to have been caused by the illness.

Legionnaires' disease is carried in water by a bacterium, legionella pneumophila, which can infect persons who inhale the contaminated water vapors. Officials were inspecting air-conditioning units, shower heads and water faucets in patients' homes for the bacteria.

"We will be able to pinpoint a common source" of exposure, said Dr. Feng-Ying C. Lin, chief of clinical epidemiology for the state Department of Health and Mental Hygiene. "But at this point, we have found no common denominator among the patients."

Lin and Robert T. Jetland, administrator of Physicians Memorial Hospital, emphasized at a news conference today at the hospital here that only one of the 45 cases had been confirmed as Legionnaires' disease.

But Dr. Arthur O. Wooddy, a member of the Physicians Memorial Hospital staff, noted that patients with the symptoms have "improved dramatically" when treated with erythromycin, an antibiotic that works well against the 20 strains of the bacteria associated with Legionnaires' disease.

Minutes from Physicians Memorial, the only hospital that serves Charles County's 83,000 residents, many workers went about their regular noon routines with little more than passing interest in the health alert.

"I'm aware of it, but I'm not alarmed," said Tommy Hayden, 58, who works at the Charles County courthouse and lives in Waldorf. "I lived in Mexico and Italy without succumbing to any fungus. I should be able to get through this."

But the alert did raise some concerns. A hot line opened Monday at the hospital for persons with questions about Legionnaires' disease received hundreds of calls and hospital officials said they were considering a second line because operators were overwhelmed. The number is (301) 645-0108.

Patients who have displayed symptoms of the illness come from all parts of Charles County, officials said. Most of the patients live in La Plata, where 12 possible cases have been reported, and in Waldorf, where seven possible cases have been reported. Twice as many men have the symptoms, officials said, and almost all of them are older than 30.

Health officials, citing patient confidentiality, refused to identify the two women who died last week or any of the patients being treated.

Charles County health officials said persons should contact their family doctor if they experience a fever of more than 102 degrees, chills, a nonproductive cough, muscle aches, loss of appetite, abdominal pain, diarrhea or breathing difficulty.

The disease, which if untreated has a mortality rate as high as 30 percent, strikes an estimated 25,000 people a year. Proper treatment with antibiotics lowers the mortality rate to 5 percent, officials said.

Legionnaires' 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.

State officials have been monitoring hospitals throughout Maryland for increases in cases of pneumonia, but had found nothing unusual as of today, a spokesman for the state health department said.

Dr. Daniel Howell, president of medical staff at Physicians Memorial, said all the county's physicians have been alerted about the problem.

Most residents should not worry about the illness, he said, because it can be transmitted only by inhalation of contaminated water. And officials emphasized that there is no evidence that the county's drinking water is contaminated.

"If you're one of the people walking around in the community enjoying this break in the weather, then you're fine," Howell said. "Enjoy it!"