The new commander-in-chief of the Argentine Armed Forces, Gen. Cristino Nicolaides, is a technically trained soldier who was relatively unknown until late last year.

In November, the hefty Nicolaides attacked the centrist Radical Party for having "convalidated situations of corruption and/or subversion," and demanded that it apologize for criticizing the military regime.

Nicolaides' outburst led most observers to classify him as a hard-liner in the military debate on whether and how soon to return to the barracks and let civilian rule return.

After decades of internal struggle, the Argentine military has attempted to maintain an orderly succession within its command structures, starting with Gen. Jorge Videla who was commander-in-chief of the Army before he overthrew Isabel Peron in 1976 and who made way for Gen. Roberto Viola at the top of the military command. Viola in turn gave up the post when he became president in March of 1981.

Gen. Leopoldo Galtieri, who was ousted from his leadership roles today, broke with that convention by continuing as commander-in-chief when he became president last December. The dual succession process resumed today, with Nicolaides in the top military post only.

Nicolaides graduated from the national military academy in 1947 and then gained an engineering degree. He was named colonel in 1970 and two years later was appointed military attache to the embassy in Paraguay, an obscure position.

He was back in Argentina for the return of the populist president, Juan Domingo Peron, in 1973. The military chafed while guerrilla organizations prospered in the chaotic Peronist years, but when Videla overthrew Peron's widow, Isabel, he unleashed Argentina's "dirty war" on the guerrillas. Nicolaides was relatively on the fringe, in charge of the 7th Infantry Brigade in the northeastern province of Corrientes.

From 1977 until late last year he headed the 3rd Army Corps, whose domain included the radicalized city of Cordoba. He participated in the brutal crackdown that ranged from book burnings to "disappearances."

In December Galtieri rewarded his ally Nicolaides with command of the capital's military region.

Nicolaides likes to project a bellicose image. During military exercises last year in the province of Salta, his aides discomfited reporters with urgings to slant their photographs and their copy. A reporter recalls a typical request: "Be sure to make him look like a warrior."