So you've traced your relatives back to the Old Country and your'e sending Christmas cards to a bunch of cousins you never knew you had. Is that all there is to it? Genealogy is the third biggest hobby in America, right behind stamps and coins, but it is going beyond the hobby status, just as it goes beyond the search for birthdates and occupations and offspring. It is becoming a national rage for social history.

Wilton Dillon, director of Smithsonian Symposia and mastermind of hte Kin and Communities program, knows that every time some newspaper runs an article about the Institution's two year family history project, he will get a blizzard of letters.

Some of these writers actually want the Smithsonian to find their ancestors for them, a somewhat impractica notion, but most just want to talk about their people.

Dillon understands. Always interested in his own family history, he knows the slightly obsessive enthusiasm of the ancestor-hunter. He has visited Palmyra, Tenn., where his father, grandfater and great-grandfather were born in the same log cabin. He has traced relatives to Oklahoma Indian territory and Lincoln, Va. He has even started in on his wife's family, taking it back to a member of Admiral Perry's party whichopened up Japan.

"There's a terrific urge to do one's own oral history," he said. "For one thing, we have new techniques: the telephone, which brings us into contact with distant relatives, and the photocopy machine and of course the tape recorder. I think oral history is even more a national passion than straight genealogy because it's closer to the feelings. It can be a very emotional experience."

He showed a reprint of an article by Eli N. Evans, "How To Interview Your Grandparents": "Ask them about their own parents, the neighborhood they grew up in . . . childhood songs . . . pets, toys and jokes . . . Ask about love, about the first time she met your grandfather, the first time they kissed . . ."

It also urges amateur historians not to shrink at unpleasant events, illnesses, accidents political fights war and depression, "Ask what the Great Depression was like for the family; whatjobs he got, His bosses and what he was doing when Pearl Harbour happened and when Franklin Roosevelt died."

Evans suggests short taping sessions and lots of repetition, for familiar tales have a tendency to change under repeated scrutiny.

Signs of the boom are everywhere: coffetable books with blown up snapshots and reminiscences: best-sellers: TV specials; conventions; heraldry doodads, professional family researchers. Some people publish their own story, as did Jack Shapiro of suburban Maryland, whose typescropted 72-page memoir beigns "I was born in Odessa, Russia. My mother never knew the exact date but would say it was about two weeks before passover . . ."

There is even a printed memoir" form, "My Personal Memory Book," by Lee Publishing Co., Box 44, Washington, D.C., with space alloted for the family tree, education facts, legal records and such miscellany as "people I have known," hurmourous & embarrassing moments" and so on.'

National Archives is holding a course in genealogical research (call 523-3183). Archives is one of over 50 source facilities for family history in the Washington area alone.

P Why is this all happening: Is it a fad, or something more?

Evans writes that "interviewing my parents and aunts made me feel less lonely somehow - no longer a practicle of sand on the beach but a part of all our family and the immigrants generation who went before and struggled, wandered, settled, loved, married and bore children. Talking about our family history provided me not only a bridge to he past but an anchor for the future."

Dilon believes it has something to do with the Bicentennial in a large sense, a national coming of age, a time for self-examination and stock taking.

"When I say family I don't necessary mean the Norman Rockwell image of Americans all beaming around the Thanksgiving table," he said. "There are all sorts of families, of course, a great variety of family experiences."

He also suggested that it could have something to do with the institutions of government "that have, quote got us into this mess" and a resulting search for other, more reliable institutions. Like the family.

In other words, being no longer comfortable with the identifying ourselves simply as Americans, we need additional ways of seeing ourselves.

"Also, it's liberating," Dilon added. "Looking into your family past can be painful, and you need to be liberated to face the hard facts. Maybe we're getting liberated as a nation by having to face so many hard facts these last few years."

Awareness of one's origins can be important for one's peace of mind, according to Dr. Murray Bowen, a psychiatrist who runs the Georgetown University Hospital Family Center. A leading student of multi-generational family relationships for 20 years, he has developed family researches into a form of self-therapy.

Often misunderstood to mean that he has patients do genealogy, he explained that he works with the extended family and especially the generation gap:

"The generation gap is part of the emotional process in all families - when you have unresolved emotional attachments to your parents you have to deal with them some way, and the mechanisms include denying the power of the family in the first place or distancing yourself form them. Most of ususe some combination of these."

It is the people who reject their families, he observed, who in later life are apt to have problems with identity, not to mention loneliness.

The attitude gets passed along from one generation to another, he said. And there is no point in trying to repair the damage by working with the children only. "You have to go back a generation instead of forward."

The families where the generations hold together are more healthy and stable emotionally, he added.

What will become of all this material being so energetically taped and typed at kitchen tables from Portland to Portland? It must be immersely useful, after all, even though some professional historians say it perpetuates distortions about historical events. With the increasing vogue-for social history-history seen in terms of how ordinary people lived and thought-family chronicles should be a great mine of raw material.

Already we know from memoirs much about the more spectacular phases of our history. Books and films like "Hester Street," "Godfather II" and "America, America" have fixed images of New York immigrant ghettoes in the antional mind. It took the Swedes to immortalize on film the settlement of our northern Midwest in "The Immigrants," but plenty has been written on the subject by Americans, notably Mari Sandoz' "Old Jules." And there are the sagas about the trek West.

But what about the others? WHat about the ones who didn't go West? What about the people who inhabited those scores of villages that dotted 18th-century maps of New Hampshire, today existing only as bits of stone fence one stumbles across in the deep forest? What about the millions who lives and died in the same town, unmarked and unremarkable?

Their stories too could give historians useful insights into, say, the causes of the Civil War, the rise of Populism, elections of Presidents, elections of Presidents and other events that seem mere abstractions themselves.

The answer is that collation of oral histories is beginning to happen. The Newberry Library in Chicago has a program to study such documents, as do Clark University and University of Alabama, among others. American University has toyed with the idea. There is an American Association for State and Local History at Nashville, and for years the Mormon church has collected generational history, patching it into a giant retrieval system.

So if your grandmother says she was in Buffalo in 1901 when McKinley was shot, get out the tape and grill her.

You are now a historian.