Writer Richard Stratton, a prote'ge' of Norman Mailer and friend of historian Doris Kearns and her husband, author Richard Goodwin, was found guilty on a drug conspiracy charge in federal court here today.

Stratton, 37, was one of 15 persons indicted in April 1982 following a raid in rural Springvale, Maine, by police and agents of the Drug Enforcement Administration that netted $1.5 million in hashish and marijuana.

Charged with "conspiracy to possess with intent to distribute" the drugs, and faced with testimony that he had headed a scheme to fly marijuana into remote airstrips in Canada, Stratton contended that he associated with drug world figures only as "investigative reporting" for his novel-in-progress about narcotics smuggling.

After the verdict, U.S. Attorney Richard S. Cohen called Stratton's contention "a sham," said the verdict reflected the "good common sense of Maine juries" and described the three-week trial as the culmination of a "major case with international implications."

Defense counsel Ira London, a Brooklyn criminal lawyer, said his biggest disappointment was that "we couldn't get a literary defense into evidence." Because of government objections, London said, he and co-counsel Marshall Stern of Bangor were unable to use the testimony of what he called "writers who have been in a similar situation," such as Hunter Thompson and Gay Talese.

Even Stratton's novel was not admissible after he abruptly decided not to testify rather than risk exposing the identity of his "confidential sources and contacts." If Stratton had taken the stand, London said, "there is no question in my mind that he would have been acquitted. Richard is basically a truthful man."

Mailer and Kearns had testified in Stratton's behalf, stressing their respect for his literary efforts. Mailer called the book "a very close piece of reporting" that "shows great knowledge of the drug trade," and Kearns said it "uncovers a world we may not want to know about."

But U.S. District Court Judge Edward Gignoux told the jury in his charge this morning that "the fact that Stratton intended to write about his experiences . . . does not provide any justification for his actions . . . and would not be a defense against this charge." After 4 1/2 hours of deliberation, the jury of seven men and five women returned its verdict, and Gignoux set a $500,000 cash bail for Stratton, finding a "very real risk that he might flee." Last summer, while free on $75,000 bail that he obtained by using as collateral his half of the 160-acre Maine farm he owns with Mailer, Stratton failed to appear for a pretrial conference and his share of the farm was seized by the government.

"I won't even attempt" to raise the bail, Stratton said from the Cumberland County Jail. He was "surprised" at the verdict, believing that "the crux of the matter is that I was not an active, willing participant in the conspiracy." But he said that the government "really wants to get me badly," and that when he is brought in for sentencing next month, "I expect the maximum" of 15 years.

Stratton is also facing drug charges in Canada, along with his wife and her daughter Michelle. A total of 54 persons have been indicted in what Toronto narcotics officers say is the largest drug case in the city's history. Among the others charged is Robert (Rosie) Rowbotham, a convicted Canadian drug figure who funded Stratton's writing project, reportedly paying him $200,000 over several years in exchange for a percentage of the royalties.