Expectations are high for construction of the Second Avenue subway, and the futuristic new subway cars that will run on it. Made from gleaming stainless steel, the cars have a range of modern innovations: round porthole windows that would look at home on a rocket ship; high-tech air purification systems that use ultraviolet lamps to kill germs; illuminated route maps on the wall; and -- incredible as it seems -- public address systems that make clear, intelligible announcements.

Sound pretty good?

It did in 1949, too, when 10 prototype cars were delivered to the New York Board of Transportation. The board planned to run the cars on a new subway line it was just then preparing to build under Second Avenue.

Of course, the Second Avenue subway was never built, and no additional cars of the same futuristic design, known as the R11, were ever ordered.

The cars cost about $100,000 each, and together the 10 prototypes became known as the ''million dollar train.'' They were not built to be compatible with other cars, though, so they could not be added to most other trains. Without a line to belong to, they remained an oddity. Orphans, they kicked around the subway system, running on a few scattered lines (the Canarsie line, the Franklin Avenue shuttle) until they were retired in 1976.

Nine of the cars were scrapped.

But one of them, Car 8013, sits on display in the New York Transit Museum today in Downtown Brooklyn, an artifact of a future that never arrived.

Until now. Maybe.

This week, the Metropolitan Transportation Authority, the eventual successor of the transportation board, signed a $337 million contract with a company that will, if expectations become reality, dig the tunnels from 96th Street to 63rd Street for the first leg of the long-awaited Second Avenue line.

''It's a longstanding municipal dream,'' said Charles Sachs, the senior curator of the Transit Museum. ''It's been planned for at least 75 years. It's always been a heady idea for enhancing the public transportation network in Manhattan.''

Heady but unlucky.

Plans for the Second Avenue line, first prepared in the 1920s, were revived in the 1940s, when the R11 cars were built. In 1951, voters approved a measure allowing the city to borrow $500 million for rapid transit projects, which was primarily intended for construction of the new line.

Years of fiscal difficulties and political wrangling followed, but no tunnels were ever dug. ''They had very high hopes,'' Mr. Sachs said of the planners who ordered the R11 cars in the expectation that they would have a line to run on. The cars themselves seem to have reflected that same optimism.

''It was a radically new design for subway cars,'' Mr. Sachs said.

When a scale model of the R11 was exhibited, an August 1948 article in The New York Times called it ''New York's subway car of tomorrow.''

With its sleek stainless steel shell, the R11 car was a stark departure from the painted and riveted steel cars that preceded it. It was not until some 15 years later, in the mid-1960s, that a full line of stainless steel cars came into use, Mr. Sachs said.

A description posted at the museum says that because polio was a concern in the 1940s, officials were looking for a way to curb the spread of germs in the subway. Earlier subway cars had conventional fans mounted on the ceiling. The designers of the R11 developed a forced air system that brought in air from the outside, ran it through ''electrostatic dust filters'' and under ultraviolet lamps intended to kill germs, before blowing it through ceiling vents into the cars.

Another newfangled feature: fluorescent lights. The description accompanying the car said, however, that the lights were considered less than reliable and were hard to replace when they burned out.

Today only the exterior of the car looks as it did when it was new. To make maintenance easier, the cars were gutted in 1964 and renovated and rebuilt inside, with parts that were standard to other cars.

A black and white photograph that Mr. Sachs retrieved from the museum archives shows one of the cars in the days before it was gutted. The advertisements along the top of the car are for Schlitz beer, Life cigarettes, and a 1949 movie starring Loretta Young called ''Come to the Stable.'' A poster invites riders to ''meet Miss Subways, Elaine Levine.''

Signs in the car indicate it was running from Brighton Beach in Brooklyn to Times Square. The rectangular windows on the sides of the car open with a crank. On the doors, above the porthole windows, is the admonition: ''Please Keep Hands Off the Doors.'' The seats are striped and upholstered in a faux wicker plastic.

On the outside, Car 8013 is almost as shiny as the day it arrived, a metallic symbol of its own bright promise.

But on the inside, the car conveys something more like dreary disappointment. The walls are two shades of a grayish, greenish blue. The fiberglass seats are hard and gray. The only sound is the buzz of the fluorescent tubes.

Photos: The last of 10 prototype cars from 1949 for the Second Avenue subway. It was clad in stainless steel, had porthole windows, and cost $100,000. (Photo by Andrea Mohin/The New York Times)(pg. B1); A photograph of the R11 car before renovation, with faux wicker upholstery and ads for Life cigarettes and a Loretta Young movie. (Photo by New York Transit Museum Archives); The exterior of Car 8013 remains as gleaming and futuristic as ever, sitting in the New York Transit Museum in Brooklyn. (Photo by Andrea Mohin/The New York Times)(pg. B2)