The 1970 census turned up only 189 noses here, a gain of 29 in a decade. But the 1980 count is expected to nearly double, because this quiet, 77-year-old vacation community now is attracting more year-around residents.

Many are early or semi-retirees, mostly fugitives from big cities. Many seem to have been frequent summer visitors or cottage owners in Bethany before they decided to transplant themselves there.

Most of the new Bethany taxpayers are couples whose children have grown and gone. Few seem to be candidates for the inactive list, however.

Early retirement from the FBI bored Joseph R. Tansey, for one, who moved from Washington to Bethany West, a relatively new community of more than 200 houses half a mile from the ocean. He said he started selling real estate "for something to do and to keep up with the inflating cost of living."

Now he has a real firm that sells, builds and handles rental properties. His wife and daughter are part of the firm. Tansey also drives half an hour to Georgetown, Del., at least one night a week to teach a realty law course at the community college there.

Thomas Hooker, a former circulation executive with the Philadelphia Bulletin, survived serious heart surgery a few years ago and decided to live permanently in Bethany Beach, where he had a summer place for years. Now 62, he lives in a new town house in the Hidden Harbor complex. It was built by Hugh Hickman and Sons Inc. on five inland acres abutting a small "turnaround" canal that runs from near the ocean to Salt Pond.

As a property owner and full-time resident (along with four others owners), Hooker keeps an eye on the daily operation of the small pool and one tennis court.

Susan and Parker Connor were Washington suburbanites who became interested in Bethany Beach real estate while vacationing there with their children. They bought a real estate office and opened a radio station in the same new building, and moved here permanently a few years ago. Parker, an attorney, still goes into Washington about once a week.

Mr. and Mrs. Vernon Dibeler had the Hickman firm build a house a few blocks from the ocean for their full-time occupancy when he decided to retire early from the research staff of the National Bureau of Standards. The Dibelers had owned another cottage near the ocean and knew Bethany Beach was right for them. Now Dibeler serves as one of the seven town commissioners and is a member of the volunteer fire department.

Dibeler is working to help keep the town as low-rise and quiet as possible. But he recognizes that the area's new sewage treatment system will stimulate more growth; nearly 50 new houses are being built each year here.

He says he was disturbed initally by the emergence of the big, high-rise Sea Colony complex on the ocean south of Betheny Beasch.

"I was among those who picketed at Sea Colony in the early days," Diebler said. "I was convinced it would bring too much traffic and noise. Now I don't mind admitting that most of my fears were overblown. I respect what has been done there and I know some people who own apartments. Sea Colony really hasn't affected Bethany Beach all that much."

Dibeler pointed out that Bethany Beach has a requirement that houses be built on lots of at least 5,000 square feet. The height limit for new construction is 31 feet.

Lot sales are strong at this seaside town, which was founded at the turn of the century by a Washington church group. Land prices range from $5,000 for developed areas a few miles from the beach to the $25,000 level near the ocean.

Most of the new houses here are built for 12-month living, while many of the cottages built in the 1940s and 1950s were three-season dwellings. Now electric heat with heat pumps, heavy insulation, double-glazed windows and air conditioning are almost standard for most of the houses, which seem to be priced from about $50,000.

However, the biggest real estate game in this area has been Sea Colony, a five-building complex that opened in 1971. Nearly all of its 835 apartments have been sold and contracts are being drawn up for a sixth building started earlier this year. Two-bedroom-and-den units start about $65,000. With 15 tennis courts and five pools, Sea Colony attracts many Washington, Baltimore and Wilmington, Del., buyers who summer there and make monthly weekend visits in the off season.