In a dirty and brawling village of the Middle East, unzoned, unplanned, choked with the sons of David returning to be taxed, the Prince of Peace was born.

Bethlehem was no "city beautiful," surely no "suburb beautiful." Yet amidst its squalor and confusion, it throbbed with life, with a rich diversity of peoples and culture. Into that scene came the new life that would change the world.

For generations now, the United States has been seeking to cordon off and extinguish its Bethlehems. We have tried to zone and regulate each thing in its neat place: industry here, shops there, rich folks here, poor folks there.

"The courteous and comfortable" among us, the Ford Foundation's Roger Kennedy notes, have gone to almost any length "to avoid daily reproach by sight, smell or sound of the unassimilated, unsocialized and uncomfortable."

We have told our aged, our students, our mentally ill that they (and of course we) are better off if every class is safely ghettoized. Any group or class of persons who fail to fit the Clairol image are to be kept out of sight, out of mind.

And in a nation of a racial and ethnic diversity unprecedented in human history, we have embraced the idea of a homogeneous melting pot instead of celebrating the collective strength of myriad individual cultures, each with its own rich traditions. Whether from Poland or Greece or Africa or Ireland or China, each group of immigrants suffered from its own first impulse to assimilate in order to succeed here. And then U.S. culture delivered a subtle, persuasive message: The heritage from your homeland has no value; you must join the amorphous mainstream of American life.

But, says Geno Baroni, the neighborhood advocate in the Carter administration, "whenever you try to force people into conformity, they rebel."

That rebellion, notable in the ethnically based neighborhood movement that gained power in the mid-1970s, now questions whether it's so desirable to be absorbed into the great majority's culture of Dick and Jane school books, advertising puffery and suburban perfection.

Instead, a new idea is abroad: that diversity in neighborhoods - diversity among age, income, ethnic, religious or professional groups - is desirable in its own right. The idea gathered strength in 1977 as large numbers of young professional people moved into older city neighborhoods, raising fears of dislocation of the poor people who live there now.

But the idea of neighborhood diversity has a compelling logic of its own.

Newly elected City Councilman John Sweet, a leader in Atlanta's reviving Inman Park, explained it this way: "One thing we value in this neighborhood is heterogeneity in age, sex, race, income. When you're in a homogeneous community, the essential strength you have is to stop things. And if a neighborhood can't defend itself, it won't survive."

But in a diverse neighborhood, Sweet said, "you catch opinions and insights of a lot of different kinds of people. You have a much higher probability of coming up with effective directions to cope with the changes constantly occurring in a city."

Inman Park first gained community strength in fighting an interstate highway that would have cut it two, Sweet noted. "We fought in the courts, in the streets, at public meetings; we got to know each other because we were being threatened. But the real metamorphosis in the neighborhood came when we managed as an organization to take what was essentially a negative movement and began to turn it into a positive movement."

Now Inman Park has its own newspaper, a credit union to finance mortgages turned down by redlining banks, a highly successful food cooperative. The young professionals who chose Inman Park's inner-city location are being poorer tenants gain ownership of their own homes.

Diversity, says Philadelphia neighborhood leader Conrad Weiler, can help promote racial integration, reduce the need for school busing, end the isolation of the elderly, "fight crime by having many different eyes on the same streets all the time." Diverse neighborhoods can put people, jobs, places to shop closer together.

Criticism of homogeneous neighborhoods - rich or poor - is mounting. Children in post-World War II suburbs, reports Edward Wynne in a new book, "Growing Up Suburban," are cut off from the diversity of the real world; forced into a prolonged childhood by their isolation, they exhibit alarmingly high rates of suicide and drug and alcohol use.

Conversely, says California Gov. Edmund G. Brown Jr., one can visit big-city, low-income housing projects and find "not one person who is a policeman, a nurse, teacher, doctor, lawyer, plumber, carpenter" - no one who is part of "the normal workplace that the rest of us are part of. And then you ask why things are going downhill?"

There's a parallel in the natural environment, says Jeffrey Smoller of the Wisconsin Department of Natural Resources. "If you have a large piece of land in a single species - acre after acre of pine, for instance - that plantation is highly susceptible to disease, pests, often fire." Diverse plantings, by contrast, provide natural barriers to pestilence and fire.

The idea of diverse neighborhoods is a "hard sell" in American today. Not only does it defy our ideas of zoned neatness, but it also arouses feelings of deep insecurity among many people in every income, race and ethnic group. Some write it off as a ploy of "trendy" young professionals who say they like the richness of an old neighborhood setting but know they have the means to move out instantly if the levels of crime or racial tension mount too high.

But if "trendy," the young professionals are also trend-setters, and may contribute strongly to life and leadership in city neighborhoods, perhaps even form deeper loyalties to the places they have chosen.

Diverse neighborhoods - building mutual respect and tolerance and understanding among peoples - may prepare us for an even greater task: to relate with sensitivity to the many foreign cultures with which we will have to cope in the global village of the next century.