Stojan Nikolic was named coach of the Washington Diplomats yesterday, succeeding John Ellinger, who resigned last week because of personal disagreements with team ownership. He is the American Soccer League team's fourth head coach in three years.

Nikolic, 40, played professionally in his native Yugoslavia and in the Major Indoor Soccer League and defunct North American Soccer League. He is the coach of the Hershey (Pa.) Impact of the American Indoor Soccer Association and said he will retain both coaching positions.

In a written statement, Nikolic said the Diplomats have "the potential to be league champions with a little help."

Washington, the 1988 ASL champion, has a 4-2 record this season and is in second place in the Southern Division. The Diplomats play the Orlando Lions at 4:30 p.m Sunday at RFK Stadium. That game will be followed by an exhibition match between Vasco da Gama, Brazil's most prestigious professional club, and Central American all-stars.

Vasco da Gama, based in Rio de Janeiro, has won 27 Brazilian championships and has supplied many players to the national team. Current Vasco members are expected to contend for spots on the 1994 World Cup team.

Former Diplomat Joaquin Canales, former U.S. national team member Hugo Perez and El Salvadoran star Jorge Gonzalez, who plays in Spain's First Division, are expected to play for the all-stars.