Ma Bell may be knocked right out of her rocker at about 11 o'clock tonight when millions of Americans, high on guilt and sentiment, take to telephones to reach their relatives.Whatever else it is, the new production of "Our Town" sponsored by The Bell System makes a sensational commercial for calling long-distance.

Unfortunately, viewers won't see a full-length version of the play because of all the less subtle commercials for keeping-in-touch that will interrupt it and because NBC has refused to let the show run past the 11 p.m. cut-off time. Even so, the "Our Town" that airs at 9 o'clock on Channel 4 is still the best and most complete ever made for TV.

Thornton Wilder's 1938 Pulitzer Prize play about "the real life of the people" in tiny Grover's Corners, N.H., after the turn of the century is, really, a gosh-darned masterpiece, one of the five or 10 American plays most likely to live into the next century.

Producer-director George Schaefer's new version does begin with uncertainty and is marred by occasional miscalculation, but when the stops are pulled out for that tear-bath third act, everything works, and we are helpless before Wilder's devices and unimpeachable sincerity.

"Our Town" may be the great white "Roots" - a celebration of smalltown Calvinist values as an idealist imagines them to have been - but it's riddled with universalities that have little to do with New England, the work ethic, good fences or good neighbors.

"Our Town" is the rare kind of classic that hardly anyone could miss the point of, and yet Wilder remains endearingly rather than painfully obvious.

Schaefer had to do considerable cutting but refrained from major revision. Wilder specified no realistic sets or props, and Schaefer has largely complied, with production designer Roy Christopher supplying a handsomely stylized town of suspended roofs and minimal furniture, consistent with Wilder's stress on the elemental.

There are two key errors. One was in giving the stage manager, who narrates the play, a map for the opening tour of the town. That is vulgar and literal.The other was in not eliminating Wilder's use of questions from actors placed in the "audience." Schaefer employs offscreen voices that, in terms of the medium's visual boundaries, make no sense.

Two large cuts had to be made after taping was completed. The first completely removed actor John Houseman, playing Prof. Willard, from the show, and the second wiped out some baseball-playing cronies of the young hero, George. The cuts had to be made because NBC wouldn't let the drama run one minute longer than two hours.

The cast for this production is fairly outstanding with Hal Holbrook as the stage manager, Ned Beatty was Dr. Gibbs. Sada Thompson as Mrs Gibbs, Barbara Bel Geddes as Mrs. Webb, and Robby Cox as Mr. Webb. When you hear Thompson read a wistful line like "It's been the cream of my life to see Paris, France," you get the feeling you'll never forget it.

The crucial young lovers are played by Robby Benson and Glynnis O'Connor, previously teamed in such movies as "Jeremy" and "Ode to Billie Joe." Benson's smokey-dreamy delivery gets a bit wimpish, but O'Connor proves herself in thee final "Goodbye, world" speech, probably the most beautiful in the play.

"Our Town" may not be indestructible, but it is nearly inescapable. The play has passed into the realm of folk literature; Hollbrook said jokingly during production that, "Half of those who will see our version will have played in 'Our Town' themselves." There were four previous TV versions, one starring Paul Newman and another that featured Frank Sinatra singing "Love and Marriage."

It's a play to come back to and NBC's programming it at the end of a long holiday weekend is wise. At about the time Holbrook ends the Grover's Corners," it will be 11 o'clock indeed, and hearts will be sighing all over the nation. "Wasn't life awful," one character will have said by them, "and wonderful."