A lot of people fire their doctors.

And when they do, says writer Joan Klein in American Health magazine, they may feel the way President Truman felt when he fired General MacArthur.

"I just fired God," Truman said.

A recently retired government official, less in awe of physicians, tells how "I changed my doctor about five years ago. I went to him for a physical. It was a factory!

"I went from technician to technician, and each time I'd wait, sitting on cold porcelain on my bare end, while the doctor was going from one cubicle to another seeing four or five people at one time. I felt I was being treated like a hunk of meat.

"So when he finally got to me, I said, 'I think I'm going to switch doctors, because everything is for your convenience, not mine.' He said he had a big patient load. I said, 'Why can't you control it?' He said, 'I get calls. I can't really say no.' I said, 'If you don't say no, then you leave me sitting on my cold behind on your enamel furniture.' "

Probably too many people stay with their doctors, however, because they're afraid or don't know how to switch.

"I want to change doctors," a young District professional woman said. "But I'm almost afraid she'll find me and want to know why I've changed. I feel guilty and embarrassed about it. I don't know why."

The "whys" are several. Among them, according to Dr. Eugene Robin at Stanford University:

* The idea that you have the right and ability to judge your doctor has not yet completely permeated the doctor-patient relationship."

* I think people do have guilt feelings, particularly if they see the doctor as a highly trained, superior person. How can you be disloyal to that kind of person?"

* "People get comfortable" with even a far from perfect relationship, and may feel, "Better your own devil than some other devil."

* When you're well, changing doctors may be easier. But "when you're sick, you often feel insecure and unable to make decisions. It's usually then that you consult doctors. It's not an easy time to change."

But it is always your right.

Doctors agree: If you habitually lack confidence in your doctor, it's time to change.

"I tell patients it's fine, it's all right, you don't have to prove your doctor has done you wrong, you don't have to give a reason to change doctors," Dr. Harry Kuykendall, an Alexandria family physician says.

"That's part of what we value in our medical care system. You can see anyone you want and don't owe anyone an explanation."

Seeing "anyone you want" may be more difficult in some prepaid, total care health plans: HMOs (health maintenance organizations) and the like. But some facilitate it, and the insistent patient can usually accomplish it.

One way to do it -- just as in seeking a consultation or second opinion -- is to do it completely in silence to your former doctor, saying nothing. This is the coward's way out, but we're all cowards sometimes.

I once did it. And I'm afraid I've regretted it since. I feel I should have said -- and hope I'd have the courage today to say -- "Doctor So-and-so, you're not the right doctor for me."

Kuykendall says: "Any time patients leave me, it leaves me wondering, Did I insult them? Did my nurse insult them? I'd like to know."

"The final test of your ability to assert yourself with your doctor is your capacity to tell him that you're leaving him and why," Dr. Marvin Belsky and Leonard Gross wrote in their book, "How to Choose & Use Your Doctor."

"Too often," they said, "patients stay in unhappy relationships that dehumanize and hurt them . . . Perhaps the doctor is located in their neighborhood . . . Or they don't believe a change will improve things. Or they hold the doctor in awe and are frightened . . . lest the continuity of their care be interrupted.

" But there are times when a doctor-patient relationship just isn't going to work out."

One patient told Belsky he wanted to leave him but felt he could not because his case was too complicated.

Belsky told him, "It's very important that you don't stay if you're unhappy," and assured him he'd send on his records and any good physician could readily grasp the situation.

"There is no situation so complicated that a patient should feel a doctor owns him," Belsky concludes.

One easy, perfectly acceptable way to tell a doctor that you're leaving -- and why -- is to write a note, stating your reasons.

What reasons do patients commonly give?

Too much time in the waiting room. Curt, cold or even rude treatment by the doctor or staff. Curt, unsatisfactory, incomprehensible or hurried explanations -- or no explanations at all -- of treatment recommendations or referrals for tests. Lack of interest on the part of a habitually bored or distracted physician.

Inability to get the doctor on the phone. Too many prescriptions by phone without a face-to-face examination. Too big a bill or, just as upsetting, an unexpected bill -- a bill for a brief phone conversation, for example, or for filling out an insurance form or, a prac- tice a few doctors follow, a bill for not showing "I want to change doctors, but I'm almost afraid she'll find me and want to know why." -- a District woman up for an appointment. The last may be particularly upsetting if it comes from a doctor who constantly makes patients wait.

Doctors may legally charge for all these practices if they think charging is justified. But they're likely to get fewer complaints if they let patients know this in advance.

Sometimes doctor and patient are just different types. Some people want a doctor to address them as "Mr." or "Mrs." or "Ms." Others think a doctor unfriendly if they're never addressed by their first name.

"I think we have to recognize that some combinations of individuals are bad for the doctor and patient," says Dr. Robert Collins, a Washington orthopedist. "To continue that kind of relationship is bad for the patient and just gnaws on the physician's ulcer."

Often -- though the patient may not know it -- a doctor is happy to lose a particular patient. Then both doctor and patient may gain.

By the rules of medical ethics and legal decisions, doctors are free to choose those they will care for. But a doctor is not free to "abandon" you if you're under treatment; he or she must give you notice and enough time to find another physician.

Changing doctors is not to be taken lightly. There are no perfect doctors -- something we have to tell ourselves again and again -- and there are people who change doctors for the wrong reasons.

But if you find yourself constantly changing, constantly doctor-shopping, the failure may be in your own expectations.