"If This Isn't Love," a new drama by Sidney Morris, cannot be faulted for exploiting its subject, the 20-year relationship between two gay men. Sidestepping sensationalism and eschewing any seaminess of act or language, it advances the notion that two men can travel the rocky road of life together as constructively as a man and a woman.

That said, it should be added that Morris' dramaturgy is fairly primitive, and his two-dimensional characters, trapped in over-explanatory dialogue, are rarely very convincing. Morris intends his play to be emotionally uplifting, but more than good intentions are required to hoist this evening out of its sophomoric rut. The gender of the two characters can't alter the fact that "If This Isn't Love" is a soap opera--replete with the usual soap operatic antics and platitudes.

For relief--intentional or otherwise--Morris can be counted on to write a periodic howler, along the lines of "Man's inhumanity to man kills me" or (my favorite, delivered in a moment of emotional upheaval) "I don't know if my heart can take it--coated as it is with Tums."

Morris' play enjoyed a modest off-Broadway run in 1982. The current production featuring Paul Malec, one of the original actors, was first staged in June at Baltimore's Theatre Closet. The Washington engagement (through Oct. 8 at the Church of the Epiphany, 1317 G St. NW) is apparently in the nature of a tryout for another assault on the Big Apple, which surely has other matters on its mind by now.

Divided into three acts--representing "The Fearful Fifties," "The Seeking Sixties" and "The Succulent Seventies"--"If This Isn't Love" follows the fortunes of Adam, a struggling Jewish actor (1950s), who begins making big money in TV commercials (1960s) and ends up a film star with a posh New York penthouse (1970s); and Eric, a timid Irish-Catholic student (1950s), who finds his calling teaching retarded children (1960s) and acquires his own school (1970s). The first act shows their fumbling attempts to establish a relationship. The second act shows the relationship coming unstuck over questions of fidelity and pride just as the couple is about to leave for an anti-Nixon demonstration in Washington. By the third act, Adam has had a minor stroke, but the two have reached a major understanding. From their balcony, they cheer the Gay Pride parade marching up Fifth Avenue.

A lot of Morris' dialogue is spent catching us up on intervening events in his characters' lives, as well as the sociological and political shifts in the climate of the country as a whole. There is a considerable amount of name- and incident-dropping. When the characters get down to the nitty-gritty of their union, it is with such less-than-felicitous observations as, "You won't rain on my parade," "I will never forgive you for making me feel like Eleanor Parker in 'Interrupted Melody,' " and "You showed me the way to paradise." (Adam also says "Mon Dieu" repeatedly, but actor Jerry Holste pronounces it "Mon Dyou.")

Neither actor is gifted enough to rise above such earnest tripe, and the performances, innocuous at best, fail to take into account the decades that are rolling by from act to act, unless pasting on a mustache and adding a dab of gray at the temples are taking account. Leslie Irons' direction tries to keep up a pretense of reality, although the minimal sets certainly don't facilitate the task. Theatrically speaking, it's all pretty elementary.

Still, even rudimentary efforts like "If This Isn't Love" can indicate a change in the sociological weather. What it is selling is the conventional aspirations of its characters, who are experiencing problems and emotions similar to those in the straight world. Not unlike "Torch Song Trilogy," last season's Tony-winning drama, it makes a case that homosexuals have as much right to an ordinary hearth and home as anyone else. That's a big step away from the torment and trauma of "The Boys in the Band." Unfortunately, "If This Isn't Love" remains a lousy play.

IF THIS ISN'T LOVE. By Sidney Morris. Directed by Leslie Irons. With Jerry Holste, Paul Malec. At the Church of the Epiphany, Thursdays through Saturdays until Oct. 8.