Witty, imaginative and supremely professional, the National Theater of the Deaf is becoming an American treasure. Its double bill of "Volpone" and "Quite Early One Morning" and other works by Dylan Thomas last night opened a brief vist to the Hartke Theater, where there will be repeat performances today at 2 and 8 p.m.

Founded 11 years ago and internationally celebrated after crisscrossing the globe, this remarkable group is rooted in mime but addressed to hearing audiences. Three skilled voices provide what one needs to know but the mime itself and the lovely gestures of the language of sign weave a spirtual spell of unipue appeal.

The "Volpone" concept would be striking withoug the group's mimetic specialty. Stepehn Sweig did the hour's adaptation from the Ben Jonson classic, recently transposed into "Sly Fox." With ingenious sets by David Hayes and costumes by Fred Voelpel, Don Redlich stages this in Chinese style, black-garbed prop people serving as stagehands as well as lingual guides.

This retrained scense of chinoiserie accents the story's brittle humor about the miser who pretends to be dying so he can reap still more gold, treasures and women. Redlich uses the expressiveness of the faces, amusingly made up, to freeze the action at appropriate points. Jonson's Venice is still there to be sure, but Marco Polo is in the Vicinity.

Ruth Langner's Sweig translation is finely used by the three speakers, Benjamin Strout, Candace Broecker and David Fitzsimmons, the latter especially adroit in hinting at, but never overdoing, the lingual variations. Though the three are speaking actors, all have worked closely with the NTD.

Many of the other performers are graduates of Gallaudet and veterans of its theater company, whose visit with "Iphegenia in Aulis" to the O'Neill Center alerted founder Hayes to the potentials of such a national company. Patrick Graybill, the slick Mosca, was on the Gallaudet faculty, where Edmund Waterstreet studied, as did most of the players.

New to the company is Hawaii's Shanny Mow, whose Corvino is beautifully achieved with striking make-up and expressions. From the Soviet Union, which also boasts serious attention to performances by the deaf, comes Dosia Skorobogatov, shose bangings and arched doorways are clearly conveyed. Under the vast garments of a humorous Voltare is a girl from Gallaudet, Carol Lee Aquiline, and the sensuous Canina and Columba are wittily done by Linda Bove and Rita Corey.

As the curtain-raser, the Dylan Thomas excerpts accent beauty in motion -- in signs for clouds, sea, sleep, waking and other shimmering images through which the Welas poet showed his passion for life. The National Theater of the Deaf gets here all too seldom, so try to catch them today.