Some postal management students are already there, in the heart of Potomac, sitting in conference rooms learning the theories and skills of mail handling and, to the horror of area residents worried about rising stamp prices, taking the occasional plunge in a large, indoor swimming pool.

But this is only the beginning. When the move from Bethesda is completed in the summer of 1983, there will be 493 students at the Postal Training and Development Institute on Kentsdale Drive, and 80 instructors, 80 contractual workers and 180 support staffers. New dormitories will be built to house the 400 students who don't fit in existing buildings.

All this is in the heart of what federal judge Harold H. Green called an "enclave of exclusivity" when he rejected a suit against the training center, a wealthy residential area where long lawns stretch down to a winding street dotted with signs warning motorists of horsemen. The postal service bought the 83-acre estate from the Sisters of Mercy in October, to replace the facilities in Bethesda. The sisters, who ran a school for the handicapped, moved out because they were "not comfortable in a place that connotes wealth and privilege," a spokesman for the order said at the time. Residents think the postal service should feel just as uneasy.

But James B. Howell, who heads the center, thinks it's perfect. The gym, swimming pool, baseball diamond and soccer field are just the thing, he said, for giving physical training to postal inspectors, who provide security for the service. And supervisors taking three-week courses can use them when they're not in class.

The postal service said it will spend no more than $28.3 million, and the General Accounting Office agreed with them that it was a better buy than Fort Belvoir, the site it regarded as the only feasible alternative, and cheaper than maintaining rented space in Bethesda. Vice President George Bush, in a letter to Delegate Robin Ficker of Potomac, also agreed.

When the sale was completed, the McAuley Park Citizens Assocications, which in more gentle times organized hay rides and caroling in the neighborhood marshaled its forces to fight the intruders. Each of its 80 members pledged $250 for legal expenses, and the group sued the Postal Service on environmental grounds.

It cited water supply, sewage disposal and transportation problems -- no buses run on Kentsdale -- but lost its case. The group hasn't given up, says president Nancy Kogan. She argues that the environmental damage to the area is clear: "There's a change in nature, from a place inhabited by four secretaries, one caretaker and seven or eight nuns, to a daily traffic pattern involving 1,000 people." She hopes an appeal will be successful.

In his latest effort against the training center, Ficker has sent a letter to every newspaper from Cape Cod to Hawaii saying that the postal service has chosen the most expensive place in the country for its main training center. He wants people to complain to their congressmen about the "Tai Mahal training resort," in the hope that funds will be cut off.

But what annoys residents more than the expense is that they haven't been consulted. Julian S. Stein, who shares what he reckons is a 500-yard boundary with the postal service, said he never received any notification of post office plans. Residents were told the property wouldn't be changed in "any way, shape or from," he said, but now he has learned that the postal service will build the dormitories on the area closest to his property.

Postal service spokesman Joe McDonald says "every legal requirement" for notifying the public has been fulfilled, including displaying notices in local post offices.

But few people on Kentsdale Drive seem to understand what the postal service plans. Many believe a par-3 golf course, tennis courts and jogging track will be built. All these were once part of plans but have been eliminated, according to McDonald. Ficker said in his letter to newspapers that the project will eventually cost $50 million.

"This is simply untrue," said McDonald.

For people like Mrs. Edward Treacy, who has lived on Kentsdale Drive for seven years, the thought of "600 men with nothing to do on a weekend, drinking a few beers" is worrying. She said that hers is a close-knit neighborhood where faces are recognized. This will now change, and she says she has already noticed an increase in traffic.

However said cars will be discouraged and shuttle buses provided. Students will be advised to avoid wandering through; the residential area, he said, but admitted he has no power to stop them.

He said that the same "luxuries" that residents complain of will make the center self-contained. A bar and lounge will help keep students within facility grounds, he said.

Frank (Nordy) Hoffman, another area resident, said such promises are meaningless. "People have to go someplace," he said. "They are going to have cars."

If the McAuley group's appeal fails, residents say they will count on Ficker's letters to spark congressional interest. "I think Congress can say 'This is not appropriate,'" said David M. Barrett, another area resident. "If you are going to spend over $20 million, the first thing to do is find the best way of spending it."