NEW YORK (AP) _ Doomed lovers, political assassins and religious fanatics bent on mass suicide all parade across the stage of the Metropolitan Opera in a stark, engrossing new production of Modest Mussorgsky's ''Khovanshchina,'' not seen here for 35 years.

The opera, which had its first performance Monday night, is set in late 17th century Russia, when the young Czar Peter (later to be known as Peter the Great) is beginning to consolidate his power in an effort to drag his troubled nation out of the Dark Ages.

The plot depicts the downfall of two groups opposed to Peter - the feudal militiamen known as the Strelsky, led by Prince Ivan Khovansky, and the arch- conservative Old Believers, led by the aged patriarch Dosifei and the young prophetess Marfa.

This might not seem calculated to make for rousing theater, but Mussorgsky's musical genius brings to life both the private passions of the main characters and their place in the sweep of history.

Part of what makes the opera seem so modern 100 years after Mussorgsky died is his refusal to depict clear-cut heroes or villains. Khovansky is a boorish tyrant, but the conniving Shaklovity who shoots him is no more sympathetic. Dosifei comes closest to a character we can admire, but as he leads the Old Believers to their funeral pyre at the opera's conclusion, thoughts of Jonestown and the perils of fanaticism come to mind.

The Met has brought this brooding masterpiece to life with a first-rate cast, led by the booming basses Aage Haugland and Martti Talvela as Khovansky and Dosifei respectively, and mezzo-soprano Helga Dernesch as Marfa.

Talvela has starred for several seasons in the Met's magnificent production of Mussorgsky's ''Boris Godunov,'' while Haugland has just drawn raves for a series of performances as Baron Ochs in Strauss' ''Der Rosenkavalier.''

Miss Dernesch belongs in the Why-has-it-taken-the-Met-so-long? category. She is a marvelous singer and actress who has had a successful career in Europe but is making her Met debut now only because the originally scheduled singer canceled. Let's hope she'll be back soon.

The production, designed by Ming Cho Lee and directed by August Everding, is austere but effective, with sets and costumes mostly in black and white with occasional splotches of red. The orchestra sounded fine under conductor Neeme Jarvi.

Mussorgsky hadn't orchestrated or composed all the music for ''Khovanshchina' ' when he died, and the Met is using a version completed by Dmitri Shostakovich in 1958. His work is considered more faithful to the composer's intention than the version done by Rimsky-Korsakov shortly after Mussorgsky died.

''Khovanshchina'' will be broadcast as part of the Met's regular Saturday afternoon radio series on Feb. 1.