The Metropolitan Opera announced that it will finally begin its 1980-1981 season next month after the American Guild of Musical Artists (AGMA) voted yesterday to accept the Met's final contract offer.

The Kennedy Center's Roger L. Stevens said that the Met will perform as scheduled at the center for two weeks beginning April 20.

Rehearsals are expected to begin Monday. Anthony A. Bliss, the Met's executive director, said "It will now take several days and thousands of telephone calls before we can announce further details on repertoire or casting, or even a specific opening date." He said that it "is very likely there will be weeks when we perform fewer than our regular seven performances." t

Among the approximately 350 AGMA members at the Met -- including solo singers, dancers and stage managers -- the 80-member chorus was the most intransigent, holding out for salary parity with the Met's higher-paid orchestra, which agreed to a four-performance week on Oct. 25. The chorus agreed to a 35-percent wage increase spread over the next four years, and the rest of AGMA accepted 37 1/2 percent. In return for giving up 2 1/2 percent in salary hikes, the chorus secured a four-performance work week.