Maryland health officials have reported an alarming outbreak of whooping cough, the sickness that can have devastating effects on infants.

The state Department of Health and Mental Hygiene is investigating a possible total of 22 cases of pertussis, as the infectious cough is properly called. The most serious outbreak is reported in Baltimore, where 12 children, most less than a year old, caught the disease in July. One infant appears to have suffered permanent brain damage, a possible consequence of the high fevers that frequently accompany the disease.

Ten other cases have been reported since March, one of them in Prince George's County. Last year, only one case of whooping cough was reported in the state.

John McAvinue, a spokesman for the health department, said that most of the affected children in the Baltimore area had not completed their immunization program. The diptheria-pertussis-tetanus (DPT) vaccine must be administered at least twice, and in most cases three times, before it can provide any protection against whooping cough. Full protection comes only after four vaccinations.

Whooping cough, which is the most frequent infant illness and largest single cause of infant mortality in several developing countries, usually begins as a persistent cough, accompanied by severe chest congestion. It is highly contagious. The characteristic "whoop" that gives the disease its name appears only after the patient's throat is too irritated from coughing to produce a normal sound.

A controversial television program broadcast last March warned parents of some risks for children who receive the DPT vaccine. It is not known if the program influenced parents who did not complete their children's immunization.