The Opera Society of Washington announced a chance in its name yesterday - to The Washington Opera - as the first step in a plan to nearly triple performances by the 1980-81 season.

Within four years, The Washington Opera plans to expand last year's season of nine performances - three productions performed three times each - to five performances each for five operas.

"There is a hungry audience for opera in Washington. We see this as a sensible rate of expansion that we can achieve." George London, the company's executive director, said yesterday in announcing the four-year master plan.

This fall a fourth production will be added to the repertoire as a firm first step.

The season opens in November with Mozart's "The Magic Flute," to be sung in a new English translation by a cast of young Americans. Donizettis "L'Elisir D'Amore" will be sung by an international cast of established artists as the second production, also in November. In February, a new work by Thomas Pasatieri, a young American composer, will receive its East Coast premiere. It is "The Seagull," based on the Chekhov play. The season closes with Puccini's "La Tosca in March.

The opera company, which has been operating on an annual budget of about $650,000 will need "close to a million dollars." London estimated on the cost of the expanded 1977-78 season. At present, the company must raise $2 from private contributions for every $1 brought in at the box office.

The Washington Opera, with its new name and expansion plans, feels that much of the new money can come from corporations and businesses.

"Major corporations were confused by the title of the Opera Society of Washington. They weren't certain that it was a professional opera company's press officer.

London and Christine Hunter, president of the board of trustees, also announced yesterday that Joan Mondale, wife of the Vice President, has agreed to serve as honorary chairman of The Washington Opera.

Since London took over two years ago, the Washington's home-grown opera company has been able to complete each season with its books balanced and every performance sold out in the 2,200-set opera house of the Kennedy Center. Last season, Dalton pointed out, about 1,000 ticket buyers had to be turned away from each production.

The problem is that every performance, even sold-out, loses money since opera is the most expensive of the performing arts. But by increasing performances of each production, the local opera company could cut per-performance losses by spreading out the cost - a more efficient way to lose money.

London and Mrs. Hunter also said they were working on a plan to get up to six operas performed six times by 1980-81. That will depend in large part, however, on the success of a major national fund-raising campaign.

The Washington Opera also hopes to have a post-conservatory training program for American singers with star potential. It is expected to be in operation by 1979 and offer young artists the chance to study with master teachers.

The timing of the announcement of expanded seasons comes on the eye of an "opera week" fund-raiser on WGMS starting Monday. The opera company hopes to raise at least $30,000 this year. Last year contributions lopped a $25,000 goal.