Two years ago, Wendell and Vincell McAllister were ready for bigger and better things. Their dreams and life-styles had outgrown their tiny brick rowhouse on Buchanan Street in Northeast Washington. So, too, they thought, had their incomes -- to about $50,000 a year.

So for months, the McAllisters stalked neighborhoods near upper 16th Street -- along the tree-lined avenues of the Gold Coast and among the ramblers and split-levels of North Portal Estates -- in search of a home and an address in one of Washington's established black middle-class neighborhoods.

The McAllisters finally found what they wanted at a price they could afford; a two-story brick home with four bedrooms, five baths, two fireplaces, cedar closets, two screened porches with tile floors and a four-room finished basement.

The home they bought is on a culde-sac in Silver Spring.

"We didn't want to move out of the District," said McAllister, 39, a tall, bearded former park policeman who sells imported automobiles in Arlington. "but the more we looked [for a house in Washington], the more discouraged we became."

The McAllisters typify black families who have changed the face of the Washington area over the last decade by overcoming their sentimental ties to one of the largest primarily black American cities and moving to the suburbs.

Recently released U.S. Census Bureau data shows that the black population in the suburbs of Washington more than doubled between 1970 and 1977, with most of the growth in Prince George's County. At the same time, the number of black middle-class families in Washington dropped 29 percent during that same period.

A study released two years ago found that blacks moved to Washington's suburbs at such a fast pace between 1970 and 1974 that they accounted for nearly one-sixth the total national increase in black suburbanites -- a figure a local demographer called "staggering."

Blacks, like whites, move to the suburbs for varying reasons, and many move directly there from other metropolitan areas when they transfer here for jobs. Some blacks, generally renters with lower incomes, are forced out of the city, displaced by more affluent singles and childless couples who buy condominiums or fix up decrepit inner-city rowhouses.

Some blacks simply don't like city life, preferring instead the generally quieter, more family-oriented environment of the suburbs.

Others, like the McAllisters, say finances and the desire to have a "comfortable" lifestyle force them to make the decision to move across the city line into the suburbs.

Like other families, the McAllisters confronted the depressing reality of Washington real estate: While their salaries had more than quadrupled since they bought their first house for $21,000 in 1967, the prices of homes in the city had increased more than that.

They hated to leave their old neighborhood, a stable community of homeowners, some with children, some elderly, near Fort Totten Park, they said.

"It was so sad when we left," said Mrs. McAllister, 38, who has been a speech therapist with the D.C. public school system for the past 14 years. "My neighbors cried."

When the McAllisters began their search for a second home, they asked real estate agents to show them properties in the city costing less than $100,000 -- a price tag that not too long ago was attached to homes at Washington's finest addresses. What they saw, however, was "unbelievable," they said.

"They were asking $145,000 for a house that literally was falling down, with electrical outlets exposed and leaning floors," McAllister said. "We saw a two-bedroom house on Oregon Avenue for $185,000. We saw houses with no air conditioning, no modern kitchens, no dishwashers, no formal dining rooms."

They bought their Silver Spring home for about $110,000, and sold their D.C. home, where they had installed wall-to-wall carpeting and a new kitchen, for about $55,000.

Today, the spacious rooms of their Maryland home have an ambience of elegance from the dragon-patterned rug to the African art objects to the portraits of Vincell and their daughter Wendy on the walls. Downstairs, Wendell shows off the area he hopes to turn into a photographic dark room.

The McAllisters are the only black family in their immediate neighborhood, though other blacks live not far away. They said they regret moving 10-year-old Wendy from her old playmates, though they added that many of their former neighbors also live in the surburbs now.

Wendy still attends school in Washington; she is a fifth-grade at the Immaculata-Dunlane school near Tenley Circle. The McAllisters have switched from a Roman Catholic church in Washington to one in suburban Maryland with parishioners closer to their age, they said.

The couple said that although they reside a few minutes outside the District border, they still feel very much a part of Washington -- very "pro-Washington," McAllister said.

They follow District politics avidly, and pointed out proudly that several current D.C. political leaders were students at Howard University with them in the early 1960s.

"I still feel ties to the District," Mrs. McAllister said. "I really don't feel I've moved out, except that I pay Maryland taxes."

The McAllisters said they are concerned that young couples are finding it harder and harder to buy the same kind of "starter" home in Washington that they were able to buy 13 years ago.

That fact has become painfully clear to many families.

Kenneth and Goldie James rented a house in Washington for 13 years near the Washington Hospital Center only a couple of blocks from where Mrs. James grew up. When they began to look for a home to buy in the city in 1977, they wanted a house that cost less than $70,000.

They ended up buying a three-bedroom, detached home in Hyattsville, joining the massive number of blacks migrating to Prince George's County over the past 10 years.

"We wanted to stay in the city," said Mrs. James, a 35-year-old accountant. "But the prices were just too fantastic, really too much."

The loss of families like the McAllisters and Jameses concerns city officials, said James O. Gibson, assistant city administrator for planning and development.

"If the city is not a habitable place for solid, middle-class, child-rearing families because of high prices and the lessened expectation of participation in home ownership, I don't think it's a healthy sign for the city," Gibson said. "There is an enormous squeeze on the families in the middle."