Bethesda is on the brink of the Big Time. Or, in the dry phrasing of county planners, it's about to enter "the first rank of urban places near the city of Washington."

The reason, of course, is Metrorail, the golden spur of prosperity that officials expect will transform the heart of the sprawling suburb into a lively miniature city.

Poised for quite some time for the big boom the subway is expected to bring, members of the Bethesda business community again have been disappointed by Metro officials' latest predictions that the Bethesda station won't open until mid-1984.

Nevertheless, things will really start to happen this fall. The dusty lot behind the graffiti-covered wall around the underground Metro station site at Wisconsin Avenue and Old Georgetown Road will begin to take shape as the town's super block. The first phase of the work is to begin next month.

Called a "gorgeous" project by a Metro board member and praised by county leaders, the development will include several office buildings, a luxurious hotel, a glass-encased arcade, a cascading waterfall, a European market and a plaza reminiscent of Rockefeller Center, with an outdoor ice-skating rink where concerts will be held during warm weather.

No less important is the revised plan for Bethesda's central business district. If approved by the Montgomery County Council at an October meeting, it should launch the next great wave of development that "will pretty much set the tone and character of Bethesda for a long time to come," said John Westbrook, chief of the urban design division for the Maryland-National Capital Park and Planning Commission.

The MNCPPC, which designed the plan for the county, proposes lifting a six-year partial moratorium to permit development of 3 million square feet around the Metro station. The new development could bring in as many as 4,000 new jobs, according to Jim Goeden, spokesman for the Bethesda-Chevy Chase Chamber of Commerce.

The heart of the plan is the already approved high-rise Metro center. Although this should entice persons to the area, planners say, it will be up to additional developments to lure visitors farther into the central business district by creating an exciting place to see and explore.

The plan proposes the transformation of Wisconsin Avenue and Old Georgetown Road into great shopping avenues, such as those in Paris and Stockholm, Westbrook said.

An architecturally striking building, perhaps similar to the Connecticut Connection at the Farragut North Metro stop in the District, is what Westbrook said should replace the Sunoco station at East-West Highway and Wisconsin Avenue, across from the Metro station project. Such a mall, incorporating an underground passage to the station, would draw persons down Old Georgetown Road to the center of Bethesda, Westbrook said.

Other new buildings, farther away from the Metro station project, the plan says, should not be as tall and should have wide setbacks from the street, with many stores, theaters and restaurants. These should make the area attractive to people both day and night.

The dominant theme of the plan is to create a comfortable atmosphere by using benches, trees, fountains, sidewalk cafes and miniparks.

New developments also should draw attention to existing features, such as the 50-year-old Montgomery County Farm Women's Cooperative, which offers fresh vegetables, homemade breads, jellies, flowers and other farm products for sale on Wednesdays and Saturdays. In warmer months, flea markets also set up there.

"One of the things we are hoping to do is to keep some of the really neat stores that are there now, like Lowen's Toy Store," Westbrook said. "We're quite concerned about losing a real institution like that."

Planners hope developers will give such stores a break on rents.

If the council approves the development plan, the decision could trigger a flurry of activity to rival the big land grab of two years ago when the price of property around the Metro station doubled in six months.

This fall, however, the scramble will be measured in blueprints and designs.

"We have some developers who have been talking to us every other month for the past three years," said Don Downing, planning coordinator for MNCPPC. "And six or eight others have talked to us in the past few months and told us they're ready to go forward as soon as the plan is approved."

The planning commission will allow 90 days for submission of plans, Downing said. But projects will not be approved on a first-come, first-served basis. If the square footage of all the proposals exceeds the 3 million square feet of space allowed for development, the commission will choose among the proposals. Downing said that possibility alarms some developers.

But the prospect also will give the county and the planning commission some leverage in persuading developers to create the village flavor that Westbrook envisions.

Westbrook admits that, initially, convincing developers to add these amenities was a struggle. "Nobody wanted to do anything we wanted," he said.

The planner's key sales pitch to developers has been William Holye White's comprehensive film, "The Social Life of Small Urban Spaces," that documents where people congregated in the plazas and parks of New York City and why.

"The first thing we do is sit the developer down and show him this film," said Westbrook.

Westbrook said that developers are quick to see that people-intense areas provide their own financial incentives because a captive audience yields more business, which in turn gives a higher return on investment, which in turn means lower vacancy rates.

The county planners' enthusiasm has spread to developers. Ralph Tasman, project director for Rosansky and Kay Construction Co., which will break ground in October on the major portion of the Metro station project, confessed: "This is the most exciting project I've worked on in my entire life."

Rosansky and Kay's $135 million share of the center will include a Hyatt hotel, office building, European market, three-story shopping arcade and the plaza, the centerpiece of the project, with its ice-skating rink and outdoor cafe.

The size of the project is monumental. "We've spent 2 1/2 years and $5 million before ever putting a shovel in the dirt," he said. Rosansky and Kay expects to complete its part of the project by the fall of 1984, a few months after Metro is scheduled to open.

The Clark Building, owned by Clark Enterprises, is expected to get under way in November if the county approves its final plan, project director Art Hanket said. The 15-story office building will include a shopping area where buses will feed the Metro subway station. As passengers get off they will see a cascading waterfall similar to the one at the National Gallery's East Wing.

Plans for the Lorenz Building, which will complete the Metro Center super block, are not final.

"Each one of the projects is really exciting," Westbrook said, "and I work with this stuff every day. . . . The sum of the whole is going to be so much better than any one of them could have been individually."