Despite strenuous objections from local health planners, two hospitals, about six miles apart, have opened in western Fairfax County in the last eight months.

Reston Hospital Center opened in November and Fair Oaks Hospital opens its doors to patients today. The test for the new institutions, according to health planners, is whether the booming communities they serve will provide enough business to keep the two operating in the black.

The 1983 decision by then-Virginia Health Commissioner James Kenley to allow the construction of both hospitals will "probably go down as the biggest mistake in years," said George Barker, associate director of the Northern Virginia Health Systems Agency, which recommended against construction on the grounds that hospital beds in the region were underutilized.

Instead, during the mid-1970s, the Fairfax Hospital Association built the Access emergency center in Reston and planned to add a full service hospital at a later date.

The association also purchased Commonwealth Hospital in Fairfax City, but later decided to close it in exchange for permission to build a more sophisticated institution farther west. That was Fair Oaks.

Association Vice President Don Harris said the hospital group chose the Fair Oaks location because it is near Rte. 50 and is accessible to Reston as well as Centreville and Fairfax City.

Meanwhile, there was unhappiness in Reston. "I was very upset that {the Fairfax Hospital Association} didn't build a general service hospital in Reston," said Martha V. Pennino, county supervisor from the district that houses both new hospitals. She worked to interest another party in making good a 20-year-old promise to build a hospital in Reston.

The Hospital Corp. of America, a for-profit group and owner of Alexandria's now-closed Circle Terrace Hospital, was happy to oblige. The firm applied to the state for permission to build in Reston.

While local health planners continued to argue that western Fairfax could support only one hospital, both organizations won over the health commissioner by promising not to add any new beds to the Washington area.

Instead, they agreed to close Circle Terrace and Commonwealth. The latter will retain its emergency room service, but the rest of the building is being converted into a nursing home.

Janet Howell, president of the Reston Civic Association, said residents initially "had a lot of misgivings" about the Hospital Corp. of America "because they were a for-profit, and we were concerned they would skim {healthier} patients and not serve the medically indigent."

So far, she said, "I think the community is really pleased. I hear good things about the service" at Reston Hospital.

One question still being discussed, however, is whether obstetrical service will be available at either of the new hospitals. Pregnant women in Reston are very anxious about traveling "down the toll road and around the Beltway to Fairfax" to deliver, Howell said.

The state has turned down applications for delivery rooms at both hospitals, but Reston is applying again, this time with strong community backing. At the same time, Fairfax Hospital, a regional neonatal care center, is seeking permission to expand its obstetrics unit.

Public hearings on both applications will be held Monday night at Oakton High School and a decision could be made by summer's end.

The two suburban hospitals, each accompanied by a doctors' office building, are similar in size and mission. They hope to serve a community of 134,300 that county planners expect to grow to 202,000 by 1995. County demographer Jeffrey Bates said the growth primarily will be among married couples in their thirties with children, he said.

The $27 million, brick Fair Oaks Hospital has 160 beds that will be used primarily for adults receiving medical or surgical care, said Administrator Steven E. Brown.

Success for Fair Oaks is "highly likely," Brown said, because the hospital came with 450 physicians who were already using Commonwealth Hospital. Reston Hospital also boasts the latest in diagnostic and treatment equipment.

Both hospitals say they plan to do a considerable amount of same-day surgery. Neither has a pediatric service nor are they equipped for high-stakes procedures such as heart bypass surgery. For those needs, patients will still have to go to Fairfax Hospital or into Washington.

Unlike Fair Oaks, the $25 million Reston Hospital faced a greater challenge when it opened. Reston did not bring patients, doctors or support staff from its Alexandria location.

"Our medical staff, board of trustees and patients are entirely new to us," Administrator James Perkins said. Admitting privileges have now been extended to 350 doctors, many of whom also see patients at Fairfax Hospital. Perkins said that, so far, 70 of the hospital's 127 beds are open and the occupancy rate is about 45 percent. He expects that to improve steadily.

"Trust has to be earned," he said.