For most of his life, Robert K. Brown was one of those guys who just drifted - from soldiering to logging and mining, selling weapons to teaching judo, construction work to guarding armored cars.

Then he saw the marketing potential in his exploits and started calling himself a "professional adventurer." Now Brown is making a small fortune telling others how to be one, too.

For the past 18 months, the 44-year-old publisher and editor of the quarterly Soldier of Fortune, "the fighting man's factual magazine," has become the chief spokesman and source of information for Americas mercenaries.

It was his Colorado-based magazine that ran an advertisement for Daniel Gearhart, a Vietnam veteran from Kensington, Md., who was looking for employment as a mercenary. Through the ad, Gearhart signed up last February with pro-Western forces fighting in Angola's civil war. He was captured by the Cuban-backed opposition after only three days in action, tried and executed. The advertisement was cited by the Angolan judge as one of the main reasons for the death sentence, and as an indicator of Gearhart's character and intentions.

Articles and advertisements in Brown's magazine also have helped the majority of an estimated 400 Americans find their way into the Rhodesian army, bolstering the white-minority government in its battle with black nationalists.

Brown, a former Green Beret and Vietnam veteran, seems almost a caricature. He is a hulking tough guy talking big-money exploits, advanced weaponry, and "kill ratios." He proudly boasts about his 14 scars from a mortar in Vietnam, and uses profanity in every sentence.

His magazine almost appears to be a self-parody, featuring articles like, "U.S. Mercs and Financiers Oust a Red Regime," and "Underwater Knife-fighting Techniques."

The advertisements are also eye-catchers, offering deals on original World War II Nazi helmets, weaponry for "men of action" and posters of barechested women fondling automatic rifles.

Yet, the classifieds are perhaps the most telling reading. One advertiser sought recruits, saying he is attempting to sell a "Complete military unit to foreign government." "Will be dirty job with little glory," the ad said. Another ad sought "mercenary work anywhere" for a man who described himself as an "ex-Marine counterinsurgency expert who spent two tours in Vietnam."

The combination apparently has some appeal. Brown claimed that there are 12,000 subscribers and 70,000 paid circulation after only five issues.

The Vietnam war appears to be the main factor that made Soldier of Fortune possible.

"Americans have recently had experience in war, a sense of involvement in the international Communist aggression. A lot of these guys came back embittered, psyched about further (Communist) expansions, like in Angola or Rhodesia," Brown said during an interview in Rhodesia.

"It was also tough for a lot of these guys to get jobs when they got back. So they're trying to market their military skills, the only skills many of them have, elsewhere."

In a recent interview with the Village Voice, Brown elaborated: "Thanks to Vietnam, the largest number of unemployed combat-trained soldiers in the world is in the United States today.That's where I foresee most of the new mercenaries coming from."

Figures purportedly from a recent readership survery show that 56 per cent of the magazine's readers are veterans and that the average reader owns $2,650 worth of weapons. The sampling also revealed that 43 per cent earn more than $15,000 a year, and that 54 per cent are college graduates.

By Brown's own admission, however, he peddles information on a field in which he has limited experience. In his first escapade in the late 1950s, Brown said he made three trips to Cuba to try to contact Fidel Castro, then a guerrilla leader. Brown said that as a college student he belonged to a group that opposed the old Cuban dictatorship. He was never able to contact Castro, however.

In the 1960s, Brown acknowledged, he almost hooked up with a plot to bomb the palace of Haitian President "Papa Doc" Duvalier; and in the early 1970s he said he negotiated with the sister of an American jailed in Mexico over an escape plan, but another mercenary group got the deal.

Last year Brown was outmaneuvered on the Angolan mercenary effort by recruiter Dave Bufkin.

Brown laughingly admitted he has never been involved in a "big-time" mercenary exploit, the type his magazine advertises and writes about.

He said his military experience has been limited to two stints in the U.S. Army between 1954 and 1957 and between 1968 and 1970, when he said he served in Vietnam as an intelligence officer commanding 12 GIs in charge of 570 Vietnamese soldiers. He says he is still a colonel in the Army reserve.

Thas has not inhibited him from Cultivating the mercenary image. One year he sent out Christmas cards with a cartoon of himself on a unicorn with a lance spearing Santa Claus. Reindeer Rudolph, Dancer and Dasher were hanging dead on hooks in the corner.

Another year he sent out "Happy Tet," cards, marking the Vietnamese new year, with a picture of himself in fatigues holding a submachine gun. Inside the card read, "Now Uncle Ho is gone . . . Beware Fidel. Look out, Papa Doc."

The mustachioed publisher is also a militant conservative, actively promoting anyone who wants to fight for the Rhodesian white-minority government, and still embittered by the loss suffered by the two pro-Western forces in Angola.

"As far as funding the anti-Communist forces (in Angola) goes, all we had to do was sponsor a few hundred mercs and pull the same ploy that Castro did with the Bay of pigs prisoners - capture 1,200 and hold them for $56 million in ransom," a recent issue editorialized.

"So we lost a magnificent opportunity . . . and now wait in a trance for the Russian bear to start gobbling again. We desperately need a backbone transplant - and in a hurry.

"The Angolan debacle is also illustrative of how the CIA has been emasculated by the Goody Two-Shoes of his country."

About Rhodesia, Brown said in an interview in Salisbury's "Sunday Mail," that "It is apparent that the black majority in Rhodesia is not hostile to whites. A significant aspect of Communist successes is their political indoctrination of the population. But here it is questionable how this type of indoctrination is taking hold.

"The black people are more primitive than the Vietnamese and their only motivation is that they want to take away what the whites have."

Readers who query him on joining the Rhodesian army are advised to call the chief recruiting officer in Salisbury to quicken the application process. Brown shrugged off the fact that U.S. law prohibits Americans from serving in any foreign army, pointing out that Americans involved in Angola or Rhodesia have not been prosecuted so far.

The motivation for starting his magazine? "Profit," he said, laughing.

Then more seriously: "There are a lot of guys who feel the (U.S.) government has lost its guts since Vietnam and they're willing to do something on their own about it. My magazine only serves as a clearing house. We're just tapping the potential of a new market. That's good business."