Fairfax Hospital, the first hospital in the Washington area to perform heart transplants, may be forced to end its heart transplant program or lose $50 million a year in federal Medicare and Medicaid funding because of new national regulations due to go into effect next month.

The deadline for complying with the new regulations, originally today, was extended for 50 days to Nov. 21 under legislation signed Tuesday by President Reagan.

While the hospital currently would not meet the criteria for continuing its program and receiving Medicare and Medicaid funding, officials there hope to rectify the situation before the new deadline, a spokesman said.

Under federal legislation passed last October, hospitals performing heart transplants must meet membership criteria set by a private group under contract with the federal government, the United Network of Organ Sharing (UNOS), based in Richmond. One requirement is that the hospital have a doctor who either has a year of formal heart transplant training and a year of experience or three years of heart transplant experience.

Fairfax Hospital has a team of three doctors who perform heart transplants, but none meets that standard, said spokesman Lon Walls. The hospital has performed seven heart transplants, the first one last December, and all have been successful, he said.

The hospital may hire a physician who qualifies under the new rules; it is discussing with the network other ways it might comply, Walls said.

Fairfax is one of six Washington-area hospitals that formed an unusual consortium and jointly received approval in January from District of Columbia health planners to perform heart transplants. In addition to Fairfax, Washington Hospital Center, Georgetown University Hospital and George Washington Medical Center have since performed heart transplants.

None of the other programs is in immediate jeopardy, said Lori Brigham, executive director of the Washington Regional Transplant Consortium. Washington Hospital Center has a heart transplant specialist who meets network criteria, and all three have kidney transplant programs that qualify them for a two-year extension of time to comply with the new rules, she said. Fairfax Hospital does not have a kidney transplant program.

The network has 264 members, of which 179 are organ transplant centers. Another 41 transplant centers, including Fairfax Hospital, have pending applications, said a network spokesman. Most are not yet in compliance with the rules, he said.

Whether the network membership rules are too stringent is a matter of debate among health experts.

"These are very stringent criteria," said Brigham, attributing this in part to the influence of large heart transplant centers on network membership rules.

But an aide to Sen. Albert Gore Jr. (D-Tenn.), who sponsored last year's organ transplant legislation, said the new standards are not overly strict and that hospitals without a certain level of experience among the staff should not start doing heart transplants. Hospitals that have performed kidney transplants have experience that is useful in starting a heart transplant program, and that is the rationale for giving those institutions a two-year extension on next month's deadline, the aide said.