Photos published this week of Nicaraguan rebels executing a purported Sandinista sympathizer have focused national attention on a 21-year-old Northwestern University student with a right-wing reputation who took the pictures.

Newsweek magazine printed Frank Wohl`s photos of an unarmed man being stabbed in the throat as he lay with his wrists bound in a shallow grave he had been forced to dig for himself. The magazine compared the incident with the shooting of a Viet Cong lieutenant on a Saigon street by Police Chief Nguyen Ngoc Loan, which aroused worldwide sentiment in 1968.

Wohl, who took the Nicaraguan photos Jan. 7, refused to discuss the incident with The Tribune.

''I`d like to talk to you but my agent says that the New York Post is willing to buy the photos for $1,500, and that it would include an exclusive interview,'' he said. ''So if the Post is willing to pay $1,500, you have to understand where I am coming from. . . .

''I try to get as much as I can; that is capitalism. Newsweek made assurances to me when I sold them the photo and allowed me some editorial control over it.''

Wohl, of North Miami Beach, Fla., is well-known on the Evanston campus, where he is a junior in the College of Arts and Sciences.

During his freshman year he was found to be keeping an automatic rifle in his campus dormitory.

''We told him that he couldn`t keep it, and he removed it,'' said Rick Williams, assistant director of public safety for Northwestern. Wohl now has an off-campus apartment.

A student editor of the campus paper, who asked that his name not be used, said of Wohl:

''He is more than a radical. He has circulated photos of himself that were supposed to have been taken in Central America. He is carrying a weapon of some kind. . . . He comes into the newsroom with rounds in his hand, rifle bullets. He plays with them like (Al) Capone did with silver dollars. He is quite intimidating.''

Last October Wohl, a member of the Conservative Council on campus, was involved in a dispute with two members of the International Committee Against Racism.

According to Antonio David Jimenez, a graduate sociology student, he and Bonnie Blustein, an assistant professor of history, were walking to the University Center when Wohl accosted them and said, ''I spent the summer killing communists like you.''

Wohl`s version of the incident at the time was that the committee people yelled at him, ''It`s too bad that you didn`t die this summer.'' Wohl said he replied, ''Not quite, but some people did.''

A fight ensued, and Jimenez was charged with battery. Jimenez said he plea-bargained and was placed on 3 months` supervision.

Blustein declined to discuss the October incident but said of Wohl:

''I do know that he walks around in a T-shirt saying, `Kill them all, let God sort them out.` I heard that he had a sticker on his door saying, `I`d rather be killing commies.` ''

''I used to think he was just a right-wing nut,'' Jimenez said. ''But I think right now his main effort is trying to legitimize the contras in this country.''

Wohl is outgoing president of the International Policy Forum, which along with the Conservative Council sponsored contra leader Adolpho Calero`s recent appearance at the university.

In a letter published in the Daily Northwestern last week, Wohl said that after protesters disrupted Calero`s talk and spattered him with a red liquid, Wohl escorted him to Wohl`s apartment.

While Wohl refuses to discuss the Newsweek photos, Robert Rivard, chief Newsweek correspondent, told The Tribune: ''He knew (his photos) would hurt the contras, but he had his price, and he wanted to make money off of it. He flatly told us it was a matter of greed, and he had his price.''