This is the story of an extended, nine-household family in Alexandria that celebrated its 25-year relationship yesterday.

In an era when nearly 20 percent of the country's population moves every year, eight households still live on North Langley Street in Seminary Valley, in the red-brick houses that the couples bought when the families were young.

The households of North Langley Street evolved into a "very rare and special family," said Noreen Poulson, who grew up there.

Yesterday, 60 of them from four generations reunited--from as far away as 3,000 miles--at one large block party, with posters, old photographs, music, food, and the charades and other games that they have been playing for more than two decades.

Cohesian in a neighborhood doesn't "just happen," said Mae McKeon, who with her husband Bob raised eight children at the corner of North Langley and Strathblane Place. "It does take working together to build this sort of a relationship. We tried from the very beginning to communicate, to bring things out in the open. It's a conscious effort."

They had moved there in the winter of 1958--the Youngs, McKeons, Strattons, Kennedys, Newhouses, Laceys, Pritschets and the Lavans (the Lees came later)--into just-completed Cape Cod and ranch-style houses. Migrants from elsewhere in the country for the most part, with few relatives here, they found that they had a lot in common, including age, outlook and, in most cases, religion, they recalled yesterday.

At the time, the area seemed like country. Some of the new residents' fellow workers at jobs in Washington, eight miles to the north, thought that the raw subdivision was "the end of the earth," said Jean Young, who lived at 321 North Langley. Today, Seminary Valley is but one patch in a quilt of subdivisions that covers Northern Virginia.

All of the women then were homemakers. Four of the men worked for the government, two were setting up dental practices and the others were self-employed. They all were young professionals, in search of the American Dream, Washington style.

One of yesterday's celebrants, Charles Stratton, a retired Veterans Administration employe, remembered that when he was ill, the neighbors took over his yardwork. Mae McKeon said that Gerry Lavan came to her rescue half a dozen times in the middle of the night, to watch her children while she went to the hospital to give birth to another.

Lavan suggested that the "spirituality" of the predominately Catholic neighborhood added to its cohesion. Lacey is convinced that it was built on "caring and sharing both the joys and the sorrows."

Poulson, 27, who lives in Vienna with her husband, said that now "I don't even know the neighbors on both sides of me. It's pretty sad, especially when you grew up in a neighborhood like this."

"Sometimes, during the early '60s, we toyed with the idea of moving and upward mobility. But by then, the bond with the neighbors had taken place," said Jean Young, who, moved to Ontario last year. Young's daughter, Terri Jardeleza, and her husband are rearing their children in the old family home.

"We do miss it, but it's not like we won't see it again," Young said of the old neighborhood. "These people are still very close friends. And that will stay with you where ever you go."