In a contract negotiated with the Kennedy Center Opera House Orchestra, the center promised not to use virtual orchestra machines to duplicate the sounds of live instruments.

The use of the electronic keyboard devices -- a cost-cutting move by some producers -- has sparked widespread outrage among musicians.

The orchestra, which ratified a four-year agreement, congratulated the center for providing leadership on the use of virtual orchestra technology. The machines sparked protests in New York, London and other places where live shows and orchestras are a mainstay of cultural life.

The debate over virtual orchestras was part of a four-day strike in 2003 by Broadway musicians. Theatrical producers had proposed reducing the number of players, to save money, and bring in a virtual orchestra. That attempt failed but has been tried elsewhere.

Virtual orchestras are freestanding computerized consoles programmed to give the sound, melody and style of a real orchestra, using a compact unit that fits into a traditional orchestra pit. A single musician plays two keyboards while following a conductor.

Tom Prince, president of American Federation of Musicians Local 161-710, said in a statement yesterday that "the Kennedy Center, by agreeing to never use the Virtual Orchestra Machine, has demonstrated its commitment to live music." Local 161-710 represents the 61 members of the orchestra.

"Although several groups in New York and Los Angeles have agreed to similar bans, the Kennedy Center is by far the highest-profile institution so far to agree to the ban," said Gregory Drone, a spokesman for the orchestra. The contract was approved by what Drone called an overwhelming vote.

Michael Kaiser, the center's president, said it was never the center's intention to switch to the use of virtual instruments. "This was not a difficult issue to resolve. The Kennedy Center is committed to the sound of a live orchestra," he said in a statement. He pointed out that the center has at times employed more musicians than needed. "During the Sondheim Celebration, for example, we used expanded orchestrations that used more musicians than most current professional productions. We always intend to use an orchestra in all our productions and presentations."

The new agreement also continued the orchestra's unique relationship with the musicians of the New York City Ballet. Four years ago, in order to bring the esteemed company back to Washington after a long absence, the center and the orchestra reached an agreement for accompanying the dancers in which each set of musicians would play in alternate years. That deal stands under the new contract.

Opera House musicians will continue to work seven weeks for ballet performances, the same guarantee as the last contract. A separate agreement stipulates that the orchestra work 21 weeks for the Washington National Opera. The basic salary for the 28 weeks is $56,800, according to Drone.