Ostensibly, "Marriage a la Mode," which opened last night at the Folger Theatre, is a pastiche of two rarely performed plays by the 17th-century English dramatist John Dryden. But unless you are a particular devotee of Dryden in both the tragic and comic modes, this curious evening is best viewed as a hymn to the theater.

From that slant, it is often a beguiling, inventive production that celebrates the excessive comportment of actors, an extravagant breed to begin with. Offstage, Dryden's characters are engaged in silly dalliance and fluttery flirtations. Onstage, they are enacting, with regal pomp and noble gesture, the doomed passion of Antony and Cleopatra. There are two worlds on display here, two distinct tones, two contrasting views of men and women in love. And shuttling between them, taking on the coloration that's required in each instance, are Dryden's obliging characters.

Actually, Dryden isn't responsible for the shuttling back and forth. The inspiration belongs to Scottish director Giles Havergal, who fashioned this ham sandwich of a drama from two of Dryden's works--the comic "Marriage a la Mode" and the grandiloquent "All for Love." Rightly recognizing that a whole evening of one or the other might prove trying, he gives us alternating slices of each. This would make for a decidedly schizophrenic experience, if Havergal hadn't also had the notion of turning the frivolous characters in "Marriage a la Mode" into actors rehearsing "All for Love."

One minute, they're hiding behind their fans, exchanging bon mots and laying plans for late night rendez-vous. Then a sober-sided stage manager rings a tiny bell on the prompt table and the actors drop their giddiness for the swollen magnificence of classical tragedy. Back and forth they go--performers doing their job, surprising us with onstage identities that correspond not at all to their offstage personalities.

The real trick, of course, is to persuade us on both counts, but the Folger production isn't quite up to the double challenge. Against my expectation, the most convincing half of the evening is "All for Love," for which the actors have resuscitated the highly declamatory delivery of grand oratory. Havergal is not looking for laughs here. The wrenching passions of Antony (Briain Petchey) torn from the heaving bosom of his Cleopatra (Mikel Lambert) are played straight, or as straight as the ornate acting style permits. But in an odd way, the exotic scenes are compelling.

What is not so convincing is the comic half of the equation, although Sherry Skinker gives a stupendously antic performance as an actress so smitten with the French language that she flatly refuses to have an intrigue, but is perfectly willing to have an "amour." When Dryden's characters are not acting, they're bogged down in those crisscrossing seductions so beloved by Restoration authors, but mildly vexing today. Dryden's repartee is not always of the first order here and it helps not a bit that much of it falls to Mario Arrambide who plays the dashing swain with a hyperintensity reminiscent of "Marat/Sade."

What salvages the backstage portions of the evening is the extraordinarily rich ambiance Havergal has conjured up. In that, he is greatly assisted by Hugh Lester's cobwebby set, aclutter with props and castoff scenery, and by the sumptuousness of Bary Allen Odom's costumes. This production is especially telling in the silent comings and goings of the actors, who massage their aching feet, confer anxiously with the stage manager off in a corner, or simply gaze dreamily up into the rafters before shaking themselves to life for an entrance.

Dryden's text doesn't ever address this strange profession of acting, but Havergal has clearly mused on it and his musings are filled with love. The very premise of "Marriage a la Mode" asks the performers to turn themselves inside out and the fun is very much in the turning. Watch, for example, Lambert's gracious leading lady drop her inbred coquetry for the gilded grandeur of the Nile, or Petchey shuck the frustrations of a bored husband for the lofty stoicism of a Roman warrior. Elsewhere, such sudden behavior would land them in the loony bin. In the theater, it's business as usual.

Skinker's frivolous actress transforms herself into Antony's wife without so much as a blink, although she can raise a minor breeze in the wings by batting her eyelashes. The offstage priss (Floyd King) becomes probity itself onstage, while Paul Norwood twists himself into the dwarfish dimensions of a pandering eunuch.

"Marriage a la Mode" may depict the tumult in two different worlds, but the real action occurs on the frontier between them.

MARRIAGE A LA MODE. By John Dryden. Adapted and directed by Giles Havergal. Set, Hugh Lester; costumes, Bary Allen Odom; lighting, Richard Winkler. With Briain Petchey, Mikel Lambert, Sherry Skinker, Floyd King, Paul Norwood, Thomas Schall, Mario Arrambide. At the Folger Theatre through April 17.