OUR GENEALOGICAL homework had paid off earlier at Donaghadee, a fishing village on the coast of the Irish Sea, noted in my wife's research as the resting place of "Matthew Gibson, an old sea captain who died in 1710. aThe grave is marked by a huge stone slab lying horizontally on four stone pillars."

Ruth and I found the eroded, almost indecipherable stone in the shadow of the Donaghadee Presbyterian Church clock tower. Surrounding it were leaning markers of other ancient mariners of the clan. Notable among these was one commemorating two later Matthew Gibsons, father and son. According to cross-reference provided by the Ulster genealogical detectives, both lost their lives on a Belfast merchant ship which "sailed from Westport, Ireland, on the 23rd day of February, 1847, bound for Philadelphia. They foundered in the Atlantic Ocean, the father aged 36, the son in his 16th year of his age."

Score another for the traditional hospitality of the Irish and their genuine interest in helping visitors from abroad try to trace ancestral links. Farm folk, shopkeepers and village passersby bent themselves double to steer us on the path to the legendary Fort Hill Farm, our prime objective. It was reputed by Ruth's records to have been occupied by succesive Gibson families from the mid-1700's to about 1900. The location was described as Knockbrecken, in the Townland of Monlough. The property was said to include a historic rath, or early Norman fort.

We stopped at a promising hilltop farmhouse near the intersection of Monlough and Knockbrecken roads. Nearby was a knoll supporting a ring of trees which Kathleen Neill's husband, Don, said could be the remains of a rath.

"Grachins!" exclaimed the lady of the farm. "I don't know of a fort around here. But do you know, there's a man down at Knockbreckan crossroad who might help you. His name is Willie Davidson, and he has lived there for years on end."

Until this year, of course. Willie had turned his property over to his daughter and son-in-law. But by good fortune, he had been visting this day and had not yet left.

"To be sure their was the ruin of a fort here," he said. "Just up the road. It was torn down a long time ago. I used some of the stones to build the house. The Gibson farm? You can see it from the kitchen window. It's just across the vale, behind that barn with the green roof. Margaret Gibson and her schoolteacher daughter live there now."

As we piled back into the car, Willie Davison loosed a parting shaft from a quiver of lifetime observation. "You look like a Gibson," he said, addressing Ruth. "Around the eyes." Ruth melted into the back seat.

As the long northern twilight faded into dusk, we pulled off the road, at the entrance to Fort Hill Farm. There was no light in the quadrangle of buildings. We knocked at the door of the living quarters. No response, except from the noisy dogs, chained to their stations around the barnyard.

The luck of the Scotch-Irish had deserted us. Crestfallen, we retreated to the car. "Too bad you must leave tomorrow," said Don, reluctantly inserting the ignition key. Headlamps of an auto came up the lane, hesitated at the gate and turned into the farmhouse compound. We scrambled like chickens across the road, startling the watchdogs as well as Margaret and Rachel Gibson on their doorstep.

" . . . trying for many years to trace the family history, and finally to you, Kathleen capsulized breathlessly.

"And I think this is the original house!" Ruth gasped.

"Well I suppose it is," said Margaret, stunned.

"Sure, I think this is lovely!" Rachel chimed in.

Lovely it was. Rachel kindled a fire in the parlor hearth as the exchange of information paraded the ghosts of generations under the low-beamed ceiling, the past met presently again and the mists of familial legend gradually parted. t

Margaret confessed she knew very little of the farmhouse history, having married into the Gibson clan. "I haven't a clue," she said. It's been here a long, long time. I have some old papers in the back of the house that might tell us something."

Among them was the missing link between Ruth's great-great-grandfather, James, who came to America in 1816, and the Ulster Historical Society's documentation of Fort Hill Farm. It fit into the time frame like the last piece of a jigsaw puzzle.

The document of record was an indenture between the Right Honorable Arthur Lord Viscount Dungannon, landlord, and James Gibson, Monlough, County Down, farmer. It was dated Nov. 12, 1801. The terms included the annual rent of 11 pounds, and 14 shillings, and the duration of the lease was for the natural lives of the tenant's children, Robert, aged 15; William, aged 11, and James, aged 9. Signed: DUNGANNON. Also signed: James Gibson (his mark).

As the third son of an illiterate farm tenant with no hope of any kind of inheritance, the younger James Gibson had little choice in planning his future. At age 23 he emigrated to Vermont, moved on to Pennsylvania and unintentionally launched a search for the hazy family connection 165 years later.

Inquires to the Ulster Genealogical and Historical Guild currently are running at the rate of 600 a month, according to Kathleen Neill. The address is 66 Balmoral Ave., Belfast, BT9 6NY, Northern, Ireland. Except for an internationl postage reply coupon available at any post office, no fee is required for the initial investigation.

If the Guild researchers find a reasonable prospect of success, there is a registration fee of $20. After that, the cost varies according to the time required to make the search, with a top limit of $175.

Many inquiries are hopeless. A prime example is enshrined in the Guild's office scrapbook: "My ancestor was Patrick Murphy. He emigrated from Ireland in 1690, probably from County Antrim. Please send his vital statistics."

"There is nothing we can do with that kind of information," said Neill. "The county in Ireland is the same as a state in the United States for administrative purposes. The minimum requirement is a precise location -- town, townland, village or parrish."

[as noted last Sunday, for those on this side of the Atlantic who wish to pursue Irish ancestry with advance homework, there is a source closer than Belfast. Donna Hotaling, executive secretary of the Board of Certification of Genealogists of the U.S. and Canada, has catalogues of the Ulster Guild research materials along with similar materials for the Irish Republic. A fact sheet telling how to order these and other publicatons is available by writing to Donna Hotaling at 2255 Cedar Lane, Vienna, Va. 22180.]