On Blue Mondays, Not-So-Blue Wednesday's and Thank-God-It's-Fridays, it now is possible to get injections of live soap opera plus box lunches at Capitol Hill's determined-to-be-useful ASTA Theater, 507 8th Street SE.

For $3.50, one gets a box lunch chosen from nine varieties, buys a cold drink and munches in one's seat as the lights go down to reveal, on stage, ". . . And the Pursuit of Happiness." On all three days there are 12:15 and 1:15 performances. At yesterday's premiere the first house almost filled ASTA's hundred-odd seats, with almost as many lined up for the 40-minute repeat.

The characters include such Washingtonians as the woman running for City Council, the teacher who can't leave home without a bottle in her carry-all and the Georgetown matron zeroing in on a caterer who's lost his credit standing with the liquor dealers.

Since life more increasingly resembles soap opera than that humdrum existence romancers once called "life," the effect is subtle. In cafeterias, one is fairly furtive about eaves-dropping on soul-searing conversations. On the other hand, watching, under ASTA's bright lights, the tremulous passions of Grace, Heather and Claire, one is perfectly free to gawk, to weep or to laugh unrestrainedly while munching cheese sandwiches, turkey or hamburger and washing same down with sugar-free fizz.

Writers Christine brim and Celia Ribando are noteworthy for their compassion toward such males as Taylor, Doug and Ben, whose failings include boastfulness, venality and unfaithfulness, those relatively lesser vices through which the real-life male now follows the example set by soap opera's reactive masculinity.

NOr is one deprived of the soap opera commerical. "Pursuit's first "message" was undeniably relevant. Whether the next step will be for our increasingly sophisticated audiences to join in with verbal advice remains to be seen.