Before dawn on a May morning in 1901, Osborn H. Oldroyd, the all-time Lincoln assassination buff, departed from the back door of Ford's theater on an 80-mile hike, following the path of the man who shot and killed President Abraham Lincoln.

"My departure was unnoticed," Oldroyd later wrote, "except by a few cats that were winding up their night's carousel."

With just as litle notice this weekend, a busload of modern-day buffs of the century-old assassination followed the escape route of John Wilkes Booth through the southern Maryland and Northern Virginia countryside.

They ranged from casual observers to serious, almost obsessive enthusiasts: people who collect bricks from any booth-related building, who regularly receive a mimeographed newsletter called "The Lincoln Log," and who spend their free time interviewing descendants and debating conspiracy theories.

Following in Osborn H. Oldroyd's footsteps, they were spending the day seeking new insights into the old history hidden just beyond the subdivisions and superhighways of metropolitan Washington.

Among their number were people like Art Loux, a 33-year-old computer systems designer for a New Jersey insurance company, who came equipped with a still camera, a movie camera and a tape recorder; and Dick Gutman, who with his wife Kellie, is compiling the most complete book of Booth photographs ever assembled. There were people like John C. Brennan, a retired Federal Reserve Board employe with eight bricks and several descendants' autographs to his credit; and Mike Kauffman, a young writer and artist who said: "The problem with these assassinations is they really bring the nuts out of the woodwork."

Along for the ride were five descendants of various secondary figures in the Booth conspiracy, including 9-year-old Danny Cox, of Oxon Hill, who harbors pro-Lincoln sympathies despite the fact Samuel Cox who is thought to be Danny's ancestor . . . helped to harbor the fugitive Booth and Booth's companion David E. Herold.

James H. Hall, a southern-born retired Labor Department official, led the tour from Ford's Theater in downtown Washington - where Booth shot Lincoln - into the Maryland countryside which, he said, was "the Confederacy without being in the Confederacy. Lincoln got one vote in Prince George's County and they're still looking for the guy . . ."

Hall, whose every word was recorded on tape by Art Loux, reflected: "Lincoln has been sort of pre-packaged as bigger than life. But he arrested the Maryland Legislature, he filled the prisons without trials. The Watergate scandal was peanuts compared to what happened during the Civil War."

To accompany Hall's narration, there were Civil War songs blaring from a speaker inside the rented yellow school bus driven by Prince George's County firefighter Buddy Bear.

Somehow, during the grueling 13-hour trip, Bear would manage to find his way along some of the most obscure rural roads imaginable. At one point, a rural mail carrier even asked Bear if he was lost. He wasn't.

He was following - so far as it is known - the escape route of Lincoln's assassin, who died of a gunshot wound in a rural Virginia barn 12 daysafter the assassination. Four people subsequently convicted as Booth's co-conspirators were hanged and a fifth, Dr. Sanuel A. Mudd, served several years in prison for treating the leg Booth had broken when he jumped from Lincoln's box in Ford's Theater after fatally wounding the President.

These convictions did not close the book on the Lincoln assassination, however. Later revelations implicated other people in the conspiracy and a reputed 18-page gap in Booth's diary raised further questions.

Numerous other conspiracies have been alleged, involving everyone from Northern cotton speculators to the Secretary of War to the Confederate government itself, with the actor Booth, of Bel Air, Md., and almost omnipresent central character.

In the generations since, there have been efforts to rehabilitate the reputations of some of those convicted, notable Mary Surratt's Traven in present day Clinton, an early stop on Booth's escape route.

The Surratt Society, which sponsored the weekend tour, has been in the forefront of the campaign to restore her good name.

Meanwhile, the far-flung members of the Mudd family have been assisuously working towards a posthumous pardon of Dr. Samuel A. Mudd, whose Charles County farm was a stopping point on the bus tour Saturday.

The Mudd descendants' immediate battle, however, is for the statefunded renovation of the rundown family farm house.

"I've taken ten years out of my life and I've gotten thoroughly disgusted," Louise Arehart, a Mudd granddaughter, told her busload of visitors, who were asked to sign a petition as they were served dougnuts and coffee by members of the Sarah Frances Mudd Sewing Circle.

A little later, during the quick lunch at Gino's in LaPlata, veterans of the Booth tour recalled earlier treks. "The first group was the most intellectual," said one. "They would all nod heads in unison when Mr. Hall spoke." On the second trip, one dissenter who believes that Booth actually escaped and lived into the 20th century simply refused to get out at certain stops as a protest.

There were no such incidents on this third annual tour, however. The only real disagreement evident was an argument over the date of the Booth photograph taken in St. Louis either in 1861 or 1862.

Similar discussions of assassination minute continued as the tour made its way into Virginia. Once there, the amateur historians were rebuffed in their requst to photograph graves at Cedar Grove, an estate whose ancestral owner had turned away the fleeing conspirators.

But just afterwards, the group hit pay dirt in Bowling Green, the county seat of Caroline County, Va. It was here, 11 days after the assassination, that federal troops learned from a captured young Confederate soldier that Booth was hiding at Garrett's farm ten miles north.

On the Bowling Green courthouse lawn, the tour group rendezvoused with Maude B. Motley, a distinguished-looking granddaughter of the Confederacy who possesses, among other things, a silver of wood said to be from the crutch of John Wilkes Booth.

While Miss Motley stood wearing a Daughters of the American Revolution necklace and holding the brass-plaqued wooden silver, several cameras clicked in unison. Art Loux filmed the event.

If Miss Motley's silver was for many the highlight of their trip, the visit to the site of Booth's death proved to be something of a letdown. For one thing, the barn where Booth either shot himself or was killed by a Union soldier no longer exists. And the site of the farmhouse is now in the middle of Route 301.

Nonetheless, they unloaded onto the road's shoulder for the traditional group picture and a hike into tick-infested underbrush to a spot marked in the past by a plain metal stake.

"Somebody's taken up the stake," announced tour leader Hall. "The stake is gone. It's too bad."

Minutes later, Mike Kauffman was busily trying to recoup by digging the earth with a garden trowel in search of foundation bricks. He found some pieces of one. Someone else found the stake a few feet away. Kauffman tried to pound it into the ground, but it wouldn't stay.

Yet as they boarded the homebound bus Saturday evening, such frustrations seemed minor when measured against their search for artifacts and truth in the spirit of the man whose biographer reflected: "Whenever the question of what constitutes a successful life arises to perplex . . . turn to the life of Osborn H. Oldroyd to find the true answer . . . in ahis life's work.