When you seek emergency medical care, it is usually because of an accident or sudden illness involving yourself, a child, a relative or a friend. a

A survey of area hospitals and doctors indicates there are several things you need to know: Where to call for an ambulance; what to do until help gets there; what you can expect from emergency personnel and, of course, what it will cost.

The first, and probably most critical, thing to know is where and when to call for help. If the medical problem could result in loss of life or limb, if there is danger in moving the person or if you are unable to move yourself or the patient to a hospital, call an ambulance.

In Maryland and the District, there is one number to call: 911. In Northern Virginia, there are three numbers: Arlington, 527-8900, Alexandria, 549-5100, and Fairfax, 691-2233.

These numers reach the public ambulance services, which provide service in true emergencies. Most of the ambulances operate out of local fire departments. There is a $35 charge for public ambulance transportation in the District, Alexandria and Arlington. In Fairfax Prince George's and Montgomery, emergency service is free. Private ambulance services, which charge about $45 a ride, depending on distance, generally are used for routine medical treatment for which the patient must go to the hospital.

When you call for help, you will need to give information to help the ambulance service find you, and to aid in treatment of the patient. Be prepared to tell the operator if the patient is having chest pains, is unconscious or has suffered a stab or gunshot wound.

Give the address and telephone number where the patient is, in case ambulance personnel need to call if they have difficulty finding you. If possible, stand outside to flag down the rescue squad.

What should you do until help arrives? In general, physicians say, unless you have special training, do nothing. Do not move the patient; do not try to treat the patient. Help is on the way.

That help, according to federal standards, should arrive in 5 minutes or less. Montgomery County reports its response time as less than 5 minutes; Prince George's 5.5 minutes. In Northern Virginia, Alexandria and Arlington report a response time of 4.15 minutes, and Fairfax reports 5 minutes. The District has not met the federal standard, but is improving. So far this year, District officials report an average response time of 8 minutes, compared with the average time of 10.2 minutes two years ago.

Be forewarned: If you do not have a true medical emergency, you may be refused service. In Prince George's and Arlington, for instance, ambulance personnel have the authority to turn down requests for nonemergency cases. Alexandria will transport patients only to emergency or critical-care units of the hospital.

"We do not transport people to regular wards or floors of a hospital," said Jerry Fair, director of emergency medical services for Alexandria.

Throughtout the metropolitan area, the services of the public rescue squads differ. Among the more sophisticated services are Mobile Intensive Care Units (MICUs), which have advanced equipment to begin life-saving measures the minute the ambluance arrives, and are staffed by teams of trained paramedics.

The District has three MICUs; Montgomery has eight; Prince George's has three and Fairfax six. All four public ambulances in Arlington and all three in Alexandria are MICUs.

Aside from Arlington and Alexandria, each jurisdiction also has regular ambulances that can handle many medical emergencies. On all ambulances, personnel are trained to stabilize the patient and get him or her to the hospital as quickly as possible.

In most cases, ambulance personnel, even those on MICUs, will allow you to accompany the patient to the hospital. In fact, it is very likely you will be needed there, particularly if the patient is a close relative, to help supply information such as name, address and pertinent medical data.

One concern of many persons is how fast doctors will treat you once you arrive at a hospital.

If you have a life-threatening emergency, you will be seen quickly -- without waiting your turn or having to fill out insurance, financial or medical history forms. And all hospitals treat medical emergencies without first finding out whether the patient can pay.

"At this emergency room, we have never questioned patients about finances," said one hospital official in the District. "They know they can be seen, leave and not even mention money."

Added an official at D.C. General, "All patients are treated irrespective of ability to pay."

All emergency rooms practice triage -- that is, they categorize cases as they arrive. The most critical are seen first; the rest wait their turn. At some facilities less acutely ill patients are referred to hospital clinics.

For nonemergency cases, the wait can vary, depending on where and when you go. When emergencies come in, average waiting times go out the window.

"Some people end up waiting three hours for a sore throat because an overdose and a heart attack come in," said Dr. Michael Rolnick, director of the emergency department at Georgetown University Hospital. "Diseases are taken on severity of illness, and when several very sick patients arrive at once, it ties up a lot of staff and the less sick end up waiting a long time."

The cost of this emergency treatment varies greatly -- but generally it is expensive. If you have medical insurance, most costs may be covered. Emergency department clerks probably will fill out insurance forms, with your help, and file those forms for you.

In the District, basic emergency room fees at several hospitals are as high as $60, or $45 to walk in and $15 to see a physician. A few are as low as $40. The price tag generally is cheaper in Northern Virginia -- a total of $48 for emergency room and physicians' fees. It is even less expensive in Maryland -- $40 for total basic costs -- where emergency room fees are regulated by a state cost-control agency.

Usually, however, there are additional costs for medication and tests, such as X-rays. If you take your cold to an emergency room, for instance, the tab easily can reach $75 to $100.

"We're in a high-cost reality of having to be prepared to deal with cardiac arrest even though we don't see much of it," said Dr. Sol Edelstein, director of emergency services at George Washington University Hospital. "We don't utilize our equipment and expertise all the time, but it has to be there and available, and it cost money to maintain."

That equipment can range from simple gauze and Band-Aids to computerized monitoring equipment that tracks a patient's pulse, blood pressure, temperature and heart rate.

All emergency rooms are staffed by doctors trained in emergency medicine, surgery or internal medicine, by residents, who are doctors training in medical specialty. Specialists (such as plastic surgeons or pediatricians) are in the hospital at all times or are on call.

One very specialized area of emergency treatment is shock-trauma medicine. Although several hospitals in this area have shock-trauma teams, only four hospitals are designated shock-trauma centers for the metropolitan area; Washington Hospital Center in the District, Suburban Hospital in Bethesda, Prince George's General Hospital in Cheverly and University Hospital in Baltimore.

A shock-trauma team includes physicians, nurses and medical technicians who have immediate access to an operating room and are trained to treat patients suffering from severe injuries or illnesses that are complicated and immediately life-threatening. Typically, such injuries stem from automobile accidents, shootings or stabbings.

While it is perhaps the most challenging and certainly on of the most dramatic medical fields, trauma accounts for only 0.5 percent of emergency room cases.

All emergencies, of course, do not require a trip to the hospital. The metropolitan area has several numbers to call for information on poisons -- these are in the front of your phone book. A telephone call to your private physician or a hospital emergency room may be all that is needed to get help with other medical problems.

Above all, physcians and hospital personnel say, be prepared for an emergency before it happens. The Red Cross offers first aid and cardio-pulmonary resuscitation courses. Your county or city health agency may have list of "What to do in case of . . . Keep emergency numbers next to your phone.

And, if an emergency occurs, stay calm and act quickly.