If this Wednesday's opening of "Oh! Calcutta!" at the Harvard Square Theater proved anything, it was that on-stage nudity--once capable of raising eyebrows at the very least--is now capable of raising yawns. But it still packs 'em in.

The show, which might best be described as a theatrical take-off on "Love--American Style," with bits of oral sex and anal humor tacked on to each skit, has played to sold-out audiences in each of its performances thus far, and has added late shows on Saturday and Sunday nights to accomodate the groundswell of demand for tickets.

Wednesday night's crowd--a predominantly middle-aged aggregation of about 1650--came away feeling slightly gypped by "Calcutta's" sophomoric mix of dated, pop-schlock insights into sexual hangups, delivered by actors in varying stages of undress.

The Cambridge City Council, which on MOnday rejected a complex proposal to "go on the record" as opposing the granting of a license to the theater for staging the show, instead passed an order to require stringent checking of age identification at the theater door before each performance.

As it turned out, nobody's I.D. was checked--perhaps because few "children" could afford the show's rather steep ticket prices in the first place. And the whole council debate on the subject apparently rattled Cambridge Mayor Alfred E. Vellucci sufficiently for him to declare afterward that "it's getting to be like Russia around here."

The council will now consider a resolution to establish a review board which will aid in the interpretation of the city's confusing obscenity laws in future cases. (A film version of "Oh! Calcutta!" was banned by the council during a run at the Orson Welles Theater several years ago.)

The show ends its Cambridge exposure on Sunday, when it will embark on a tour of Middle America, perhaps in search of some sensibilities it can more effectively offend.