"Loose Ends" covers nine years, and that's exactly what it seems to take at Arena Stage, where Michael Weller's new play last night had its premiere for a run to extend through March 11.

This represents a reunion for Weller at Arena, where his "Moonchildren" made its 1971 bow also under Alan Schneider's direction. Again the settings and costumes are by William Ritman and Marjorie Slaiman.

After a false Broadway start, "Moonchildren," which had been introduced in London as "Cancer," had a long, appreciated Off-Broadway run. By including "loose" in his title, Weller seems to be anticipating criticism. At least one can credit him for wisdom.

For Weller has written in his eight scenes (which ignore 1976) the sort of play in which actors constantly begin making exits, then return to not say what they should have been saying all along.

It has been bruited that here Weller is exploring what happened to those young folk of the '60s who occupied him in "Moonchildren." These are not the same characters of the earlier play; indeed one wishes they had been, for they were a frisky, believable lot.

These characters are a mess of cliches who behave like those of the movies of the 1940s. While they talk around subjects, they never get to them. These moonchildren have not entered the late '70s; they've been going back to the time when Lana Turner, Phyllis Haver, Toby Wing and Sonny Tufts were trying to catch up to Joan Crawford and Fred MacMurray.

The story centers on Paul and Susan, who met in 1970 on a Bali beach after he had finished two years in the Peace Corps and Susan was rolling around the world far from the comforts of Denver with her impressionable pal Janice.

It is love at first sight and, as seems mandatory at Arena this winter, the nudity here is twice as nude as that in the Kreeger's "Curse of the Starving Class." For here, for no reason whatever, both Paul and Susan are nude. Doesn't anyone realize that nudity is old stuff now?

Paul is idealistic and has contempt for his brother Ben's worldly ambitions, though willing enough to drink his Dom Perignon. He wants the simple life, like making movies in Boston. And Paul wants babies.

Susan wants no part of babies. She goes off to become upwardly mobile in New York, which is, after all, close enough to Boston to make one wonder why Paul would complain about being away from her for six months in one of their interminable non-conversations. If not the Eastern Shuttle, why not Greyhound?

Filtering in and out of their lives are a couple who have too many babies (from a particularly deadly father) and the further adventures of Janice, who takes up with a religious nut she met in an ashram and later with a more worldly sap.

"Loose Ends" is loose, indeed, but one cannot, should not, say this about Kevin Kline's performance as Paul. To the last dismal scene he pours vitality and intelligence into the role.A very fine actor, he appeared at Ford's in the days when John Houseman's company graced its stage, and in "On the Twentieth Century" his outrageously funny hero won him last spring's Tony.

The case can be made, and no doubt will be, that "Loose Ends" is telling it like it is with deep, allusive meanings. Non-communication is a plague for many. (But rarely for people worth listening to on a stage.) Women's liberation is greatly to be wished. (But smart women have been liberated for centuries.) The world is changing. (Then, why don't Paul and Susan change along with it?) Nudity is not shocking. (But pointless nudity is juvenile.)

Earnest as she is as Susan, Roxanne Hart is a Ph.D. in the dramatic art of the Semi-Windmill Sweep; every line she punctuates with hands out, fingers spread, forearms twirling. Her sheer wasted energy is enough to light every corridor, room and broom closet in the Pentagon.