As night falls on North Portal Estates, a doctor jogs down Tulip Street. There is a great deal of slamming of car trunks as briefcases and dry cleaning are taken in. A woman in high heels walks from the direction of the Silver Spring Metro station. Three children playing on a lawn clipped twice a week gawk at the unusual sight of a police car in the neighborhood.

This is the big city, but it is also the premier neighborhood for Washington's blacks. For such upper-middle-class families, this neighborhood's cachet exceeds even that of the Gold Coast of homes on 16th Street.

The neighborhood is 214 detached houses with garages, large yards, swimming pools and country-like roads at the northern tip of the District between 16th Street and the hillsides of Rock Creek Park. Houses here sell for about $175,000.

"It's a suburban setting in the city," said Ronald Brown, a partner in the law firm of Patton, Boggs & Blow and former chairman of the University of the District of Columbia. Brown lived in the neighborhood for nine years, moving last year to a townhouse west of the park.

"If you look at patterns of how blacks began to spread out in the city, they didn't go everywhere," he said. "They didn't go west of the park. They didn't want it said they were going to live in an all- white area now that they had some money. North Portal Estates is as far as you can go without being west of the park."

The result is a neighborhood dominated by black professionals: doctors, lawyers, funeral home directors, beauty shop owners, ministers and local officials such as City Council member Charlene Drew Jarvis; William Rumsey, director of the city's Department of Recreation; former school board member Vicki Street; Joseph P. Yeldell, head of a computer operation for the city; Dr. Arthur Hoyt, acting director of the city's public health service; and former police chief John B. Layton.

This is also Bishop Walter "Sweet Daddy" McCullough's neighborhood. He heads the United House of Prayer for All People on Sixth Street, a few miles and half a world away in the low- income Shaw neighborhood. For a few weeks at year's end, the man who is known for walking down the aisle in robes of royal red as parishioners press money into his hands, decorates his house for Christmas in trails of flashing lights and ribbons.

The festive house has few neighborhood children to admire it, though, because North Portal Estates has few children. There are no playgrounds, no schools, no community centers and only a few basketball hoops in driveways.

Evelyn Jones, a real estate broker and North Portal's Civic League president, said six families moved into the neighborhood in September and October, but only one had children.

"The father is a lawyer and he told me he wanted his children to grow up relating to other families where they don't have to apologize for what they have . . . where they have positive black role models."

"My son and his wife are the only family below 30 in the neighborhood," said Jones. "'We have quite a few people in their late 40s, 50s, 60s, some in their 70s . . . I'd say 25 percent of the people here are retired."

Most of the blacks, now the dominant group in the neighborhood, came to the area in the late 1960s and early 1970s as wealthy Jewish people that built the neighbohood died off.

"The neighborhood is still interracial and some Jewish families are still here," said Vickie Street, "but it is mostly black now."

When a family moves into North Portal Estates, it is buying prestige but also pressure to cut the lawn, keep the gutters clear and curb the dog. Harry Jones, Evelyn's husband and head of the local Advisory Neighborhood Commission, said he has visited some neighbors about lawns and loose dogs.

"If (Evelyn) asks and nothing is done, then I'll come by too," said the retired colonel in his house on Tulip Street. "It happens, but it doesn't happen often because people here are aware of their responsibilities."

Those responsibilities seem to include watching and watching out for each other. "Whenever anyone moves in there's a welcoming party in the back yard somewhere," said one woman who has lived here about eight years. "Really, its more to see who they are than to welcome them: You know, what does he do, does she work, who are they? It's not like people get rejected, but North Portal wouldn't be North Portal if anybody lived up here. We want to be able to say who lives up here."

When the investigation began of James Denson-- who used to live on Verbena Street -- for misusing money in the D.C. Chamber of Commerce treasury, it was the talk of the neighborhood. Robert C. Lewis, then Alcohol Beverage Control Board chairman, now appealing his 1982 conviction and sentence of 6 months in the federal penitentiary for taking bribes, was the talk of the winding streets, as was Yeldell when he was indicted for bribery and conspiracy and later acquitted.

"I think people made more of a fuss about them because they lived in North Portal Estates," said Evelyn Jones. "A lot of it was jealousy."

"This isn't Adams-Morgan with block parties and parades," said Vincent Cohen, "but everybody watches out . . . we know our neighbors. When we go away the neighbors pick up the papers and keep an eye on the house."

Almost every house has the tiny bright lights by the doorbells and the decals in the windows that announce an alarm system. But crime is not a problem in the neighborhood, police say. In the six-week period from Sept. 19 to Oct. 30 there were no robberies, two burglaries, no stolen cars.

Charles Cleveland, the policeman who was responsible for cruising through North Portal Estates one day, said, "People up here are as polite and helpful as they can be. They're influential downtown; they have the low (auto) tags, but they're always helpful to me . . . I was up here when they had that party for the mayor in August behind the Yeldells' and the Rumseys'. That was a real nice party."

Although the residents may be prominent, they don't always get their way. A recent crusade by the civic league had to do with the lawn on East Beach Drive that borders North Portal.

Three years ago the National Park Service decided to let the lawn grow to create a natural habitat for insects and animals for a research project. The civic league found it unsightly and complained of asthma problems.

The park service offered to send a researcher to the civic league's next meeting to explain the experiment, but the league declined. They wanted the grass cut. The park service did not budge.

The three-year experiment is scheduled to end this year and Evelyn Jones says if the grass is not cut now, "I'll cut it myself."