After 20 years as a nurse, Shirley Knowles looked at her salary and her chances of promotion and decided to leave the field. She now earns more than $25,000 a year as a health systems analyst for a McLean computer firm.

Cathy Grannon had hoped to use the skills she had learned in nursing school to help direct the care of her patients. But after four years on the job, she quit -- to go to medical school and become a doctor.

Suzanne Hayes, a nurse for 15 years, became fed up with the awkward hours, that kept her from her children, and quit to become the director of a health policy research project.

"I would never have left hospital nursing if the hours had been better," she said. "But I would put in the long hours, endure the physical and emotional stress, then look at my paycheck and realize I had given much more than I received.

"I have pressures and responsibilities in my new job. But I'm paid well. And if there's unfinished work at the end of the day, I can work on it the next morning. In nursing, everything had to be completed or a patient might die."

Each year, thousands of nurses walk away from their profession. They complain that their hours are too irregular their authority over patient care too limited and their wages too low (starting at $10,000 here). At the same time, increasing numbers of young women, who once would have chosen nursing because it was one of the few fields open to them, are entering fields that previously were dominated by men -- and that are more lucrative.

The result: a shortage of nurses at nearly 80 percent of the nation's hospitals and nursing homes, according to the American Hospital Association. The number of nurses who graduated last year was down 2 percent from the previous year. And of 1.4 million licensed registered nurses in the United States, nearly one-fourth no longer practice nursing -- at a time when more and more people are being hospitalized, for longer periods of time, according to health policy experts.

Local hospital officials generally contend that their patients do not suffer when the hospitals have nursing vacancies, and, in fact, area health planners say the hospitals have too many beds anyway. But for the last year, the hospitals have been operating close to capacity, and some nurses on the job say they often do not have time to provide the care their patients deserve.

Nursing homes, which generally require nurses to do more physical work for considerably less pay than they would receive at hospitals, have found it even more difficult to keep enough nurses.

"We usually cannot complete with the wages paid by hospitals," said Wayne Chapman, personnel director for Manor Care, which operates five nursing homes in the Washington area and 23 nationwide. "So we try to attract nurses whose primary motivation is not money, but providing a personal service."

While most area hospitals were unwilling to provide details of their individual staffing problems, they conceded that it has become increasingly difficult to hire nurses -- even in an area that has 12 colleges with nursing programs. Their particular problems include:

Prince George's General Hospital closed 65 of its 650 beds earlier this year because it had vacancies for 159 nurses -- one-third of its ideal staff size.

The Camelot Hall nursing home in Arlington, which opened in March, was forced by the state to wait five months to open the last 60 of its 240 beds because it did not have enough nurses.

The Washington Hospital Center temporarily closed three operating rooms in its surgical complex recently when it could not replace nine Filipino nurses who quit when they did not pass the licensing exam, according to some nurses assigned to the operating rooms. A hospital spokesman confirmed that the nurses had left, but denied that any rooms had to be closed as a result.

In the most recent issue of Checkbook, a Washington area consumers guide, a survey of 349 local registered nurses rated Surburban Hospital in Bethesda and Capitol Hill Hospital the worst among the area's 33 major hospitals in nurse staffing levels. A Suburban Hospital official said the hospital was working on the problem, while a Capitol Hill official discounted the report.

"I personally know of two major Washington hospitals that have had to close beds recently because they have not been able to attract enough staff," said Steve Lipson, executive director of the D.C. Hospital Association. "The closed beds mean that some patients who need nonemergency medical care will not receive it as quickly. A hospital operating without enough nurses means that the nurses on the job are being stretched to exhaustion as they are required to care for larger numbers of patients for longer hours." Lipson, however, refused to identify the two hospitals he was describing.

"There was a time when women entered the field of nursing because they wanted to provide personal care for the sick," said Mary Callahan, acting director of nursing at Prince George's General. "Now nurses come into the nursing field expecting to be paid well and to have a lot of personal contact with the patients. But they soon find they are spending very little time with the patients and can earn much more money in other types of work."

Nationally, the average annual salary for a full-time registered nurse is about $13,000. In the Washington area, nurses earn between $10,000 and $21,000 a year, depending on their experience and speciality.

Many hospitals, faced with the daily problem of covering their shifts, have had to turn to nurse registeries of "pools" -- essentially private agencies that supply the names of nurses for hire.

Hospitals can telephone the rent-a-nurse agencies on short notice to hire the extra nurses they need for a given day. But the convenient service comes at a high price: Hospitals must pay the agencies two to three times the going hourly rate for nurses.

Nurses employed by agencies can earn nearly double the salary a hospital would pay them and can request -- and usually get -- the hours they prefer to work.

"Most of the nurses who come to work for us don't like the rotating shifts of hospital work, they want to have weekends off and they are looking for higher pay," said Cindy Gale, manager of Hospital Temporaries, a nurse registry organized three years ago. "In a sense, we're the net that keeps more nurses in the profession, because we can give them what they're looking for."

While hourly wages for registered nurses and licensed practical nurses at nursing homes average $5 to $7 an hour and $7 to $9 an hour at hospitals, nurses hired through an agency can earn up to $12 an hour for night or weekend work.

For example, Hospital Temporaries -- which has grown from 200 employes in 1977 to 450 today -- charges hospitals $21 an hour to refer a nurse trained to work in an intensive-care unit. The agency, in turn, pays the nurse about half of that.

Howard University Hospital, which needs 80 nurses to meet its desired staff level of 551, must hire 45 to 50 agency nurses a day to keep its staff level up to the hospital's minimum standards, according to Gwendolyn Webster, the director of nursing.

D.C. General Hospital, which also needs 80 nurses to bring its staff up to its optimal level of 668 nurses, hires about 30 temporary nurses each day. But even with three agencies under contract to supply them, the hospital often cannot get all the temporary employes it needs, according to director of nursing Ed Marshall.

"That means we simply have to operate that day short-staffed," Marshall said. "This does not have an impact on patient care, but no one is neglected. sWe end up having to postpone some elective surgery. We might have to pull specialty nurses to do work as staff nurses. And nurses don't have the time to comfort and reassure patients as much as the nurses would like."

Ann Burrows, a nurse since 1971, currently works on a general medical ward at D.C. General, where she and another nurse are responsible for 16 patients. One day last week, Burrows said she worked 16 hours straight because the hospital was short of staff.

"As a professional nurse, I have a commitment to make sure my patients get the highest level of care possible," Burrows said. "But any nurse who has worked more than eight hours is not going to be at her best. The problem is worse when there aren't enough nurses. You only have time to give the patients their medication, say a quick 'hello' and move on."

Dot Parry, a 13-year veteran who works at D.C. Village, the District government's home for the elderly, is responsible for 28 patients in one unit. "A lot of the people are elderly and handicapped. There is not enough time and help to turn the patients to prevent bedsores, and some patients don't get regular baths. I do the best I can, but a lot still goes undone."

In an effort to recruit nurses, and to encourage their staffs to help find them, area hospitals have begun a number of incentive programs, ranging from substantial pay raises to attractive education benefits to "bounties" for each recruit.

"Some of our nurses became a little upset when the hospital started using agency nurses who were earning much more money, with less knowledge about the hospital and less responsibility," said Callahan of Prince George's General. The hospital now has created its own pool in which nurses seeking additional work can get it at the same hourly rate agency nurses receive.

The hospital also offers a $1,500 bonus that is shared by the new nurse and the employe who finds her, if the nurse stays for a year. D.C. General pays employes $50 for each recruit they find and another $200 if the nurse stays a year. Greater Southeast Community Hospital has a similar program, with a $200 bonus for the employe at both the beginning and end of the year. In the Southeast program's first three months, the hospital has paid out $5,800.

George Washington University Hospital, meanwhile, has set up a new "merit increase" pay plan that rewards nurses who perform well with salary increases. The nurses are the only university employes who can get merit increases like these, according to a university spokesman.

But sometimes all those incentives aren't enough -- and other employers know it.

Earlier this year, for example, the Long and Foster real estate firm advertised specifically for former nurses who wanted to sell real estate. The company's ad in the Feb. 6 edition of The Washington Post praised former nurses as "some of our most productive . . . agents." "Make more money. . . . Work the hours you want, and your life will be better."

"What we've found is that nurses make super real estate salespeople," said Brian Logan, manager of Long and Foster's Capitol Hill office. "They're intelligent, they know how to deal under stress and they know how to make people feel comfortable. That makes them perfect for real estate."

Yet there are some nurses who stay, like the 48-year-old Parry at D.C. Village.

"I would like to leave nursing, but I've been told that conditions are lousy wherever you go," she said.