Dressed in a pale green surgical gown and mask, William Harryman walked into an operating room the other morning at Fairfax Hospital and -- with scalpel balanced delicately in his right hand -- removed a short section of a patient's leg vein to be used in her coronary bypass surgery later in the day.

Norman Riendeau, stethoscope resting on his white jacket, moved busily from one examination room to the next at the Oxon Hill Continual Care Clinic, seeing and treating about 25 patients by day's end.

At the Shaw Community Health Center, in inner-city Washington, Anthony L. Hinkson saw 20 patients, diagnosed their illnesses, ordered tests, prescribed treatment and suggested medication.

Although these men look, sound, and work like physicians, they are not.

They are among a growing new breed of health care practitioners called physician assistants, who generally can perform about 70-to-80 percent of the services normally offered by a doctor. Until 15 years ago, their profession, which requires them to work under the supervision of doctors, did not exist. Today, they number more than 14,000 nationally; there are about 100 of them in the Washington area, up from 37 in 1978. By 1990, experts predict, there will be 21,000 physician assistants.

PAs, who earn a national average income of about $20,000 a year, provide a wide range of care including such diagnostic and therapeutic procedures as patient histories, physical examinations, preventive and followup health care, patient education and counseling. Some, like Harryman, can perform minor surgery.

In 14 states (none of them in this area) PAs can write prescriptions for drugs -- except for narcotics and certain other controlled substances.

In sustaining its slow but steady growth, the profession has overcome a number of obstacles, including much of the skepticism and resentment among some registered nurses and physicians who feared the PAs would take their jobs or that they would be held responsible for errors committed by the new practitioners.

Pockets of resistance remain. In New Jersey, for example, PAs can practice only in federal institutions such as prisons and veterans hospitals, and in Virginia, PAs are restricted to working only as surgical assistants in hospitals. Medicare and Medicaid cannot reimburse doctors for work done by their PAs because such services were not contemplated in the original legislation.

Federal experts in health care delivery see a promising future for the profession and say that the presence of physician assistants in the nation's health care system is likely to improve the quality of health care and reduce overall costs.

The idea was born in the mid-1960s, when doctors were in short supply and some ex-military corpsmen of the Vietnam era were looking for a way to convert their training into a livelihood.

With a class of only four ex-military corpsmen and the notion that physician assistants could help to upgrade the quality and reduce the cost of health care in rural and inner-city America, Dr. Eugene A. Stead Jr. established the first training program for PAs, at Duke University, in 1965.

By 1971, the U.S. government had stepped in with $1 million in grants to help expand the training from one program to 12. By 1980, the federal money had grown to $9.1 million, supporting more than 50, usually two-year PA training programs that graduate some 1,500 new PAs each year. Women comprised 44 percent of the formerly all-male preserve.

When William Harryman was graduated from college 10 years ago he had his degree in biology and his eye on a career in medicine. But after weighing the time and expense in training to become a doctor, he decided to become the next best thing: a physician assistant.

"After training for two years in a surgical specialty program at the University of Alabama, I was able to do many of the things surgeons do after 13 years of training," saidHarryman, 33, who earns more than $30,000 a year as one of two physician assistants employed by cardiovascular surgeon Dr. Edward Lefrak.

"My job is to do the routine preparations for the major surgery,"Harryman said. "For bypass surgery, I usually remove a section of vein from the leg to have it ready when Dr. Lefrak is ready to begin the work on the heart.

"When the major surgery is over," Harryman added, "the surgeon leaves and I sew the incision. Ibasically act as another set of eyes and ears for the doctor. I can help to screen out some of the minor details that I can handle. That leaves him free to concentrate on the more important work."

When he first opened his family clinic in 1972 at its present location at 6188 Oxon Hill Rd., Dr. Mark H. Pillor said, he hired several physicians who were expensive and provided patient care that did not meet his standards.

"Most of the doctors I hired were such turkeys that the patients wouldn't come back for follow-up treatment," Pillor said. "Then I heard about the PAs and decided to hire a couple."

Pillor, who currently employs Norm Riendeau and another PA, said he is pleased with the results.

"In many instances, PAs are better than a lot of physicians I've worked with -- especially in treating trauma," he said. "The PA is trained to diagnose, suture, make up a cast. They are eager to read the latest books and stay up on the state of the art. They are very meticulous."

Recently, Pillor was vacationing and Riendeau, 31, a 1975 graduate of PA training at George Washington University, was manning the clinic under the supervision of Dr. Glenn Edgecombe.

"About 80 percent of any general practice consists of minor cases -- the colds, cuts, bruises," said Riendeau, who earns about $28,000 after six years of experience. "Those are the kinds of cases I see. The more serious ones are still seen by the doctor. And the doctor reviews and signs the charts after I have completed treatment of a case."

Anthony Hinkson, 31, who earns about $19,000 as a PA in inner-city Washington, was graduated from Howard University's PA training program in 1979. It and GW's are the only two programs in this area.

Routinely, Hinkson said, he treats patients with such illnesses as hypertension, arthritis, diabetes, common colds, asthma, allergies and rashes.

He turned to the profession after graduating from Howard with an economics degree and finding "that the jobs available to me did not pay very much," said Hinkson, whose wife is a physician.

"Having a PA is like having another physician on the staff, except the PA doesn't require as much pay," said Dr. Spurgheon K. Hawthorne, Hinkson's supervisor. "The physician assistant saves the doctor a lot of time in many instances, because the PA has the time to talk with the patient and get a more thorough background of the illness."

The medical establishment in this area is more mixed in its reaction.

Angelo Troisi, executive director of the 600-member Prince George's County Medical Society, said that his organization has left the approval or rejection of physician assistants up to individual doctors.

"We feel that the marketplace is the place to decide whether the use of PAs is or is not appropriate," Troisi said. "Any doctor who feels a PA is a help should go ahead and hire him. But that doctor should remember that he's ultimately responsible for the PA's actions."

On the other hand, "the Washington, D.C., area already has one of the nation's highest concentrations of physicians," said Dr. Lewis Biben, president of the Medical Society of the District of Columbia, which has taken no official position on PAs. "We've never been convinced that we really need a lot of physician assistants here.

"We believe the basic practice of medicine should be reserved for physicians," added Biben, whose organization has 3,300 members. "I personally don't think physician assistants are adequately trained to practice medicine. If they want to practice medicine, fine -- let them go to med school."

There are sterner variations of that attitude in places across the country. In addition to the restrictions in Virginia and New Jersey, opponents of physician assistants are pushing, through the Medical Association of Georgia, to shut down the two physician assistant training programs in that state. They argue that currently there is not enough supervision of the assistants by physicians.

There also has been some resentment and animosity among nurses toward PAs, particularly in New Jersey. Nurses there successfully have fought to keep PAs from practicing anywhere but in federal institutions because they would "duplicate many of the services already performed by nurses, but at a much greater cost," according to Virginia Treacy, labor director of the New Jersey State Nurses Association.

Melinda Carter, president of the D. C. Nurses Association, said: "We haven't had that much of a problem with them in this area. But there are still occasional questions of whether PAs and nurses receive equal pay for equal work, and whether a nurse should blindly follow the instructions of a physician's assistant."

Training programs for PAs -- which can cost as much as $5,000 a year for each of the two years -- are accredited by a committee of the American Medical Association, and physician assistants must pass a certification examination given by the National Board of Medical Examiners before they can practice. Persons entering PA training normally are required to have a bachelor or master's degree in a science-related field.

While some physicians' groups have contended that the use of PAs does not improve the quality or reduce the cost of health care, the American Academy of Physician Assistants, the profession's national organization, argues that PAs have contributed to major improvements in health care quality and that by using them, health care costs can be reduced as much as 46 percent.

"We believe the use of PAs is the most cost-effective way of providing quality health care in this country," said Peter Rosenstein, executive director of AAPA. "Current estimates are that it costs about $100,000 to train a physician. The cost of producing a PA is about $15,000. While the doctor is still in training, the PA can be out in the community providing quality health care."

Last year, a study issued by the Graduate Medical Education National Advisory Committee predicted that the United States will have a surplus of 70,000 doctors by the end of this decade if medical school enrollments remain at current levels.

"Some members of the medical profession fear that since there may be a glut of physicians in a few years, PAs may take a lot of their jobs because PAs cost less," Rosenstein said. "We maintain that since it costs less to train PAs, why not cut back on doctor training programs?"

During times of fiscal belt tightening, some health care experts say, the real question is how much quality medical care can be obtained for the fewest dollars.

"A PA can do up to 80 percent of the physician's workload," said Arlene A. Granderson, chief of the resources development section of the U. S. Public Health Service's division of medicine. "They generally have adequate training to provide excellent primary health care."

"If we look at salaries, we see that the average doctor earns between $60,000 and $100,000 a year, while physician assistants earn less than half that -- somewhere between $20,000 and $30,000 a year," Granderson said. "The bottom line is that PAs have made better health care available. And there are some indications that many patients are more satisfied with the service they get from PAs."