Each year, more than 77 million people in the United States are treated in emergency rooms, according to a study by the American Hospital Association.

"It is important to tell a dispatcher exactly what is wrong with a patient when you are calling for help," says Capt. Mary Beth Michos, emergency medical services officer in Montgomery County.

"If a person has chest pain, difficulty breathing or abdominal pain," she continues, "let them lie in a comfortable position and don't give them anything to eat or drink. In the case of an injury, unless something in the immediate environment is threatening, don't move the person."

Since April, in addition to sending out ambulances, dispatchers in Montgomery County and other Maryland jurisdictions have been giving step-by-step instructions over the phone in cardiopulmonary resuscitation (CPR) and in how to clear an obstructed airway.

Area rescue agencies are observing Emergency Medical Services Week, which began Monday.

The Maryland Department of Fire and Rescue Services will give out free medical information kits that contain a medical history card.

For more information in Maryland, call 251-2465. In the District: 673-6744. In Northern Virginia: 642-0708. The American College of Emergency Physicians offers a free Emergency Medicine First Aid Poster. Write: Communication Dept., McNeil Consumer Products Co., Camp Hill Rd., Fort Washington, Pa. 19034.