George Washington University has raised its medical school tuition next fall to $15,000 a year for all students, a 27 percent increase that puts it slightly ahead of Georgetown as the most expensive medical school in the United States.

The raise is the latest in a series of increases that have more than doubled the cost of becoming a doctor at GW in just five years. During that time, the school has struggled to meet its soaring expenses without a special D.C. government subsidy that was ended in 1976. Grants from the federal government also have steadily shrunk while laboratory costs and salaries have mushroomed.

"I've stopped using words like outrageous of mind-boggling to talk about tuition," said Dr. L. Thompson Bowles, the GW medical school's dean for academic affairs. "I just don't know of any other way private schools can deal with inflation except by escalating tuition. We don't like it, but costs are going up all over the place. How long can you keep it up?"

To pay the bills, GW officials said, many students are going heavily into debt, which now often reaches $75,000 before they graduate. About one-third of the school's 600 students finance their education by joining the armed forces or enrolling in the federally financed National Health Service Corps, which requires a year's service in an area with a doctor shortage in exchange for each year's tuition received.

Several medical students said one effect of the high cost of their education would be to raise the fees they charge when they begin private practice, which because of long training usually does not happen until after age 30.

"A lot of people start out in medical school as very liberal and very idealistic," said Scott Keeler, a third-year student from Denver. "They don't want to charge high prices, but with the size of those debts and all the time they lose [in training], they're forced to do it . . .

"I'm going to charge a hell of a lot of money because I know a lot of people my own age who are out in the world, earning $25,000 a year, buying condominiums, while I'm sitting here struggling. I hate to be so mad about it, but when they go into my office, they're going to get nailed."

Another student, already $60,000 in debt in his third year of medical school, said he expects to borrow $20,000 more for tuition and living expenses in his final year.

"Sure, [the latest increase] hurts," he said. "But when you're this far in the hold another few thousand or so doesn't really matter. Maybe I don't have a very idealistic way of looking at it, but when I get out I'm not going to go down to Appalachia in family practice. I'm going into something that pays a lot of money early on."

Last year the median net income of U.S. physicians ranged from $57,690 for general practitioners to $115,230 for orthopedic surgeons, according to a survey by Medical Economics magazine.

Even though it is the first to announce a $15,000 annual tuition, George Washington's medical school is far from the only one that is expensive.Georgetown University, which plans to announce its decision on new fees in March, already charges $14,750 tuition for medical school. Elsewhere, Albany College in New York and the University of Puerto Rico both charge $12,000 a year, while four other medical schools also charge more than $10,000.

According to the Association of American Medical Colleges, average annual tuition this year is $7,892 at private medical schools while state residents at public schools pay an average of $2,108.

Both figures are more than double the averages for undergraduate colleges, which generally do not have the large amount of expensive equipment, high-paid faculty, and tiny ratio of students per teacher found in the medical schools. At George Washington University, for example, under-graduate tuition is scheduled to rise next year to $4,100, up from the current $3,400. The cost of books, supplies, and living expenses for medical students ranges from about $3,500 to $10,000 a year.

There are 126 medical schools in the United State -- about half public, half private -- enrolling about 65,000 students. Over the last two years, average tuition at both types of schools rose by about one-third, the medical college association said.

One exception to the trend is Howard University, which receives heavy federal support even though it is privately controlled. Medical tuition at Howard now is $2,600, an increase of just 8 percent in two years.

Besides lacking state aid, which is common for private medical schools around the country, George Washington and Georgetown also lack large endowments to keep tuition down. Johns Hopkins Medical School, which is heavily endowed, charges $5,900 tuition, though this is scheduled to go up to $7,150 next year.

Until 1976, both George Washington and Georgetown received $5,000 per student from the District of Columbia budget to hold down medical tuition. The payments, which had regularly been voted by Congress before home rule, were opposed by the District of Columbia government because few D.C. residents attend the two schools.

General federal aid to all U.S. medical schools has dropped from $2,100 per student in the early 1970s to $600 this year. The Carter administration proposed eliminating the grants on the basis of projections that the United States soon will have an oversupply ofphysicians.

Some of the loss in these grants has been offset by the Health Service Corps, which started just seven years ago and now is spending $66.8 million for 5,055 medical school scholarships.

"There's still a great need for physicians in primary care in the inner city and rural areas," said Charles Fentress, public relations director for the medical colleges association. "But the more indebtedness [medical student] incur in their education, the more prone they are to go into the big buck fields or else we're in danger of becoming an educational system for the sons and daughters of the wealthy with the lower-middle class crowded out. It's staggering."