Joan Micklin Silver's second feature, "Between the Lines," an episodic romantic comedy about the staff members of the Back Bay Mainline, a prospering "underground" weekly in Boston, is the most likable and encouraging American movie to be release so far this year.

Ironically, the picture's strengths, weaknesses and overall appeal seem to derive from the fact that there isn't really much that needs to be read between the frames of "Between the Lines," which opens today at the Avalon 1 and a unit of Roth's Tysons Corner. It's a cheerfully transparent, accessible entertainment.

Silver and screenwriter Fred Barron, who presumably drew on his experiences as a reporter with The Boston Phoenix and The Real Paper for "Between the Lines," may be criticized for presenting the characters and milieu superficially. But the crucial compensation is a sparkling young cast, whose fresh personalities and winning performances offer a source of pleasure and human interest worth savoring for its own sake.

You might as well see "Between the Lines" promptly. The performers given particularly arresting and attractive opportunities - John Heard, Jeff Goldblum, Lindsay Crouse, Bruno Kirby, Jill Eikenberry and Lewis J. Stadlen - are likely to become stars or indispensable character actors in American films within the next few years. The careers of Gwen Welles, who has already made some impression in Robert Altman's films, and Stephen Collins won't suffer either, although the inability of Barron and Silver to invest much humor or affection in the ASP lovers they play makes them the weak link in the ensemble.

If you skip "Between the Lines" now, you'll probably be trying to catch up with it in a year or two, right after one or more of these relatively unfamiliar names has been "discovered" by the major producers and judged safe to cast in a movie with a large budget and large pretensions. At $830,000, "Between the Lines" cost peanuts in conventional Hollywood terms.

Perhaps directors named Joan are slightly ahead of the competition. John Heard, who should emerge from Joan Silver's movie as a potential new Dustin Hoffman - and better yet a Dustin Hoffman purged of masochism - was subsequently cast by Joan Darling in her first feature, "First Love," which also stars the presumptive new Robert Redford, William Katt of "Carrie," Silver's one casting boner - recruiting Michael J. Pollard to impersonate a mumbling little hanger-on called Hawker - throws her astute choices into bold relief. Watching Pollard stumble around, one can't help thinking that if this represents the spirit of the '60s, it's high time to push ahead with the personalities of the '70s and '80s.

One of the appealing aspects of the group assembled at the offices of the Mainline is that moviegoers have an opportunity to discover their own types. I'm not certain if Silver and Barron planned the effect ingeniously or lucked into it, but "Between the Lines" can be incidentally enjoyed and exploited as a test of personality preferences. You may be able to learn a thing or two about your date by observing which type or types at this fictional newspaper seem to turn him or her on.

Although Joan Silver has yet to evolve a distinctive directing style, she has gained appreciably in skill and assurance since making a barely adequate debut on "Hester Street." In her new movie she demonstrates a light touch that could become humorously distinctive. And her lack of an obviously assertive directing ego is not necessarily a fault. It may account for the responsiveness and generousity that appear to distinguish her work with young performers.

Silver does seem to have a reconizable thematic and sentimental tendencies. The characters in "Hester Street" were trying to assimilate to a strange culture. The characters in "Between the Lines" face a change of status: The independent if low-paying publication that has nurtured them during a youthful period of counter-culture activism is slowly but surely becoming a victim of its own success. The question is whether the members of this young Old Guard can find and sustain a vocation for themselves on a Mainline that has entered the cultural mainstream.

Once again, Silver is working with a comic fable about social adjustment and assimilation. While she's too worldly and intelligent to dismiss any of the characters as unconscionable sellouts, she betrays a sentimental partiality for the least aggressive or manipulative types, just as she did in "Hester Street." It's no an unqualified partiality, perhaps because Mr. Silver and her husband Ray, who produced both "Hester Street" and "Between the Lines," came to movies after several years in business. They have a reputation for driving very hard bargains when distributing their own productions.

Still, the director's romantic leanings definitely incline the movie toward an intimate, affectionate view of the couple played by Heard and Lindsay Crouse - Harry, the paper's erst-while star reporter, who seems to have burnt himself out, at least temporarily, and Abbie, the staff photographer, a pleasant, gutsy young woman whose career is shaping up just as Harry's threatens to fall apart. Despite their conflicts and anxieties, there's never a serious doubt in our minds about the fundamental compatability and amiability of harry and Abbie. They're meant for each other even if they haven't quite got it together.

The opportunistic and dependent types that Collins and Welles are meant to embody, respectively, remain outside the scope of the director's imaginative sympathies. One feels no rapport with them. Silver gets off the ground: Stanley, the paper's officious advertising manager, played by Stadlen, has an endearingly unrequited crush on Lynn, the indispensable secretary-receptionist-mother hen, played by Eikenberry. Preposterous as Stanley is, he retains an integrity and vulnerability that are appealing.

The most impressive performers are Heard and Goldblum. It is going to be a dreadful waste if these two young actors do not get the starring opportunities their skills and personalities deserve. Goldblum, cast as a freeloading, slightly manic, wonderfully inventive rock critic called Max Arloff, takes brilliant advantage of the film's richest comic role. He has an unusually sexy, explosive humorous presence, evident in his stunning brief appearance as Clyde Baxter, the hot-headed young actor in Paul Mazursky's "Next Stop, Greenwich Village."

Max is not a hot-head, but there is a constant undercurrent of desperation in his joking and finagling that Goldblum seems peculiarly adept at expressing. One gets the impression that Max is probably the most irresponsible of journalists, but he is an irresistible spontaneous wit. The funniest scenes in the film depend on Goldblum's ability to portray this spontaneity: Max's appearance at a dorm to speak on the topic, "Whither Rock?," and his upstaging of a "conceptual artist" who threatens to bust up the office.

Goldblum has a quicker tempo than anyone else in the cast, and it seems to take a while before Silver finds an editing rhythm that adjusts to him and enhances what he's doing. Max's privileged position as the resident crazy genius is no doubt projected by keeping the character out of the romantic conflicts. Goldblum is free to beam at coeds and groupies with idyllic, uncomplicated lust.

Goldblum, who is lanky and talk does acquire a comic sidekick of sorts round-faced, diminutive Bruno Kisby as David, who wants to escape the classified department and make waves as an investigative reporter. Kirby has one blissful interlude in which he pursues a dangerous interview subject, a local hood nicknamed "The Duck," around a nightclud, quacking at him until he's given an appointment.*