NEW YORK (AP) _ Gabriela Benackova, who made an impressive Metropolitan Opera debut last year in the title role of ''Katy'a Kabanova,'' is an equally remarkable Mimi.

The soprano sang the role in the Met's first ''La Boheme'' of the season on Monday. It was also Dwayne Croft's first Marcello at the Met and Mark Oswald's first Schaunard. John Fiore conducted his first ''Boheme'' at the Met, being deferential to the singers.

The performance was dedicated to the memory of Dorothy Kirsten, the much loved soprano who died last week. Kirsten made her Met debut as Mimi in 1945.

This ''Boheme'' stressed youth. The four students in their garret, Luis Lima, John Cheek, Croft and Oswald, sounded, looked and acted like high- spirited, penniless young men. Benackova and Nancy Gustafson as Musetta also sounded young. Renato Capecchi, as the landlord in Act 1 and Musetta's wealthy beau in Act 2, swept along with the youthful style.

Benackova has a sturdy frame and can provide volume when needed. But she was entirely convincing as the consumptive Mimi. Her tone is beautiful and the sensitive shadings and colorings that she brings to it add to the beauty. Usually, at the end, Mimi lies down and dies and one doesn't feel a jolt of emotion until Rodolfo realizes she is dead and bursts out in anguish. As Benackova sang Mimi's last words and the other singers stood or sat with bowed heads, she made that very moving.

Lima as Rodolfo has a nice shine to his tenor voice. But he often sang passionately, without much variety of dynamics. His last-act duet with Croft was very good. His pitch wavered at times.

Croft has an attractive, warm sound. Oswald sounded good and added a little high-spirited business in the garret which got laughs. Monday's was a very receptive audience, quick to respond to humor and special artistry.

''La Boheme'' remains one of the most melodic operas by the master melodist Puccini. It's an opera that doesn't have to be sung by famous people, only by good singers with the zip to be young, in love and broke in Paris in the 1840s. And Franco Zeffirelli's third act snow scene remains one of the most beautiful sets the Met owns.