Pianist Brett Duggan of New Orleans won the first prize in this year's Johann Sebastian Bach International Competition, which had its finals yesterday afternoon in the Lisner Auditorium at George Washington University. The prize of $4,000 and a variety of concert engagements, including a two-month tour of Germany, was awarded to him by a panel of three judges, whose names were not made public until the end of the competition.

They were: Alfonso Montesino, a Chilean pianist who is a professor at the University of Indiana and a winner of the London Bach Prize; pianist Edith Azenfeld, a professor at the Freiburg Music Academy and the Salzburg Mozarteum; and Irving Lowens, performer, music critic of The Washington Star and former dean of the Peabody School of Music in Baltimore. Duggan's score was 98.67 out of a possible 100 points.

Second prize went to Kari Miller of Bloomington, Ind., and the third prize to Douglass Finch of Toronto. A fourth prize, not usually given in this competition, was awarded to Joanne Kong of San Antonio, who emerged from the semifinal round in a three-way tie for second place. A special award for the youngest pianist to reach the competition's semifinals was given to 25-year-old Rebecca Plummer of Brookline, Mass.