WASHINGTON -- William Steck, a violinist who performed under some of the most eminent conductors of the latter half of the 20th century and served as concertmaster of the National Symphony Orchestra for nearly two decades, died April 13 in Alexandria, Va. He was 79.His death was confirmed by his wife, Ann Steck.From his appointment as concertmaster in 1982 until he stepped down in 2001, Mr. Steck was a familiar and essential presence at NSO performances at the Kennedy Center in Washington and on tours around the world.Violin in hand, he would appear on stage after other orchestra members had taken their seats. He would face the audience, bow on behalf of the ensemble, then turn to his colleagues to begin a rite of orchestral performance: the oboe's sounding of a pure A and the tuning of each section in turn.A concertmaster is second in importance only to the conductor.While an in-demand conductor may lead his or her orchestra in only a portion of its concerts over a year, the concertmaster is almost always present. The duties are wide-ranging and include acting as a liaison with the musical director, lassoing the often-wild string section and performing violin solos.Mr. Steck "plays with excellent technique and beguiling lyricism," Washington Post staff writer Joseph McLellan wrote in 1986. "His cadenzas, with the orchestra silent, are graceful and beautifully formed, and they probe deeply into the inner workings of the music."Vern William Steck was born Feb. 18, 1934, in Powell, Wyo.The family settled in Philadelphia, where Mr. Steck studied at the Curtis Institute of Music. He graduated from the Philadelphia Musical Academy in 1952 and received a master's degree in music from the University of Texas at Austin in 1957.Steck was brought to Washington by Mstislav Rostropovich, the celebrated cellist-conductor who was NSO music director from 1977 to 1994.In the 1970s, Mr. Steck scored his first appointments as concertmaster with the Dallas Symphony under Max Rudolf and the Atlanta Symphony under Robert Shaw.