Connie McDowell divides the world into two groups: Those who think she and her husband Scott are "absolutely crazy" and those who "wish they had the guts" to do what the McDowells are doing.

Six months ago, the 40-year-old "ex-housewife" and 41-year-old retired Coast Guard pilot set off on what one genealogy expert calls "the family historian's dream." They gave their furniture to relatives, leased their San Francisco home and hit the road in a 1958 Greyhound bus -- converted into a comfortable motor home -- complete with stereo, microwave oven and computer.

Destination: "Everywhere and anywhere," says Scott McDowell, "where we can trace our ancestors."

So far they've visited dozens of cities from Portland, Ore., to Union City, N.J. -- stopping in town halls and libraries, foraging through census schedules and land records, talking with telephone operators, newspaper editors and the oldest people they can find in an effort to fill in the ever-expanding branches of their family trees.

"I've always wanted to know where I came from," says Scott McDowell, who is tracing about 65 different surnames in his ancestry and is writing a book about one, the Jaggers. "Ever since I was a kid, and my parents teased about how our family was started by an Irish priest and an Indian princess, I've wanted to know about my ancestors."

Connie McDowell's interest in genealogy started about 20 years ago when her grandmother gave her a family history she'd been compiling and a diary written by McDowell's great, great grandmother.

But neither McDowell began searching their roots in earnest until shortly after they married in 1975. "I brought home some genealogy charts from the library," recalls Connie McDowell. "(Scott) got all excited and pulled out all his family history stuff."

In 1976 they crossed the country five times in a van, stopping in city halls and courthouses along the way to root out obscure ancestors. "We both discovered we loved to travel and were fascinated by family history," she says. "We started to dream about doing this permanently."

After Scott McDowell's retirement in 1979 (his last commission with the Coast Guard was the same as Alex Hailey's) they both got real estate licenses. In two years they had earned enough money so that, with Scott's pension, they could finance their dream.

The bus cost $32,500 ("plus a lot more we put into it") and gets about nine miles to a gallon of diesel fuel. They tow a compact car--"Have you ever tried to find a parking place for a bus?" -- and budget about $200 per month for fuel.

"If we use up our fuel allowance," says Connie McDowell, "we just stay put." If all their money runs out, "we'll be Kelly People or get some kind of job until it builds up again."

The McDowells park at the homes of friends and relatives across the country or stay in campsites. On a recent trip through Washington to research at the National Archives, they stayed in the driveway of Paul and Sara Andereck's Fairfax home. They met the couple through a Genealogical Computing newsletter the Anderecks publish.

Relatives who originally thought the McDowells were "cuckoo," says Connie McDowell, now think "it's great." Among their newly-converted fans are their six children -- they each have three teen-agers from a previous marriage who live with ex-spouses.

"The kids are fascinated, too, by their own ancestors," says Scott McDowell. "It's history that's personal. Hearing about what your great, great uncle was doing at the same time Lincoln was building log cabins makes history a lot more vivid than it is in a classroom."

"You really learn what life was like," adds Connie McDowell. "The diary my grandmother's grandmother wrote in 1848 talks about traveling with their belongings in a wagon and walking on foot from Indiana to Iowa, watching the railroad being built and avoiding places with fresh graves because that meant a measles epidemic.

"We traveled that same route, saw the same landmarks she was describing. It was awesome to think they could travel that distance. And I got a kind of strange deja vu feeling . . . like I'd been there before. It was really very beautiful."

Connie McDowell has traced her family back about 10 generations to the Coffins who came in 1642 to Nantucket Island, Mass., from Devon, England. Scott McDowell has traced his lineage back about 18 generations to an English farmer, John Scott.

The bulk of his research has been with the Jagger line (his mother's maiden name is Jagger). He has traced the family back to John Jagger who came to America in about 1635 and has between 45,000 and 50,000 descendants -- some of whom, McDowell hopes, will want to buy his book on the Jaggers when it's finished.

"I know it won't make the best- seller list," concedes McDowell, who has had no formal genealogical training. ("I just get down and do a search the same way we did a rescue search in the Coast Guard".) "But I'll get it published even if I have to do it myself. Then 100 years from now if one of my descendants wants to know where they came from, it'll all be there."

Although neither has uncovered any horse thieves in their ancestry, the McDowells have found "a whole lot of dirt farmers" and some "unusual characters," such as:

* Ancestors who "missed the boat." Two boats -- the Mayflower and the Speedwell -- left from England the same day. The Mayflower sailed into history; the Speedwell sprang a leak and returned to England. Scott McDowell's ancestors were on the Speedwell.

* Bo'swain Parks, who crossed the Delaware with George Washington.

* A young boy from the Rennick family who was kidnaped by Indians in Virginia. He was raised as an Indian and became an Indian chief.

* The first Supreme Court justice of New Jersey.

* Editor of The Cincinnati Inquirer.

Discovering these ancestors, says Scott McDowell, "has been fantastic . . . as exciting as I'd imagined. We didn't do this on a lark. I spent the first 22 years of my adult life working 70 to 90 hours a week, getting moved every two years.

"There comes a time in everyone's life, I think, where they want to know where they came from. So when people ask me why we're doing this I say, why not?"

While the "roots search" is now their primary goal, both McDowells say they're open to traveling in new directions. "At this point," says Scott McDowell, "everything is an option."

"We may find some place we want to settle," says Connie McDowell. "We almost bought an old Victorian home in Cape May (N.J.) to turn into a Bed and Breakfast. We're open to just about anything."

But when people ask, "We tell them we're going to do this for two years. But that's just because they're more comfortable with the idea of a time limit."

"We'll do it until we get tired of it," says Scott McDowell. "That just might be forever."