Lawrence Kasdan’s likable semi-screwball comedy “Mumford” has two big pluses onits side. In tackling psychotherapy, a subject Hollywood has traditionally treated witha quaking solemnity, it sustains a tone that is refreshingly commonsensical andirreverent.

The movie’s enigmatic hero (LorenDean), who renamed himself Mumfordafter the town to which he has movedto start a new life as a therapist, isalmost as astonished as his clients areby how quickly he is able to changetheir lives for the better.

But as he admits halfway into themovie, he is a charlatan with notherapeutic training. The credentials onhis office wall are as bogus as hisname.

In creating a heroic therapist who turnsout to be a fraud but still ends up agood guy, “Mumford” is paradoxicallysubversive. While the movie appears tobe enthusiastically pro-therapy(Mumford’s intuitive, offbeat approach to people’s problems works wonders), it is alsoanti-therapist in its implication that in the age of “Oprah” any sensitive person who is a goodlistener could conceivably establish a successful practice without the benefits of training orcertification.

The film’s other big plus is Mumford’s endearing star client, Skip Skipperton (Jason Lee). Abushy-haired billionaire man-child whose company produces 23 percent of the world’smodems, Skip is the very model of a computer nerd who is richer than God.

A perpetual adolescent, Skip likes to whiz around the town on a skateboard. Theheadquarters of his company, Panda Modem (named after his favorite animal), has its ownelaborately contoured skateboarding area.

If “Mumford” were a ’40s movie, you could imagine Skip being played by the gangly youngJames Stewart with every other phrase out of his mouth a quaveringly sincere “gosh” or “awshucks.” (Mumford would have to be played by Cary Grant.)

But Skip isn’t quite that naive. He’s canny enough to recognize that women have pursuedhim for his money but pure enough at heart not to be tempted. He is also desperately lonely:so lonely, in fact, that he has set about devising a technological solution to his romantictravails. His top-secret work in progress is a line of robotic sex surrogates that are virtuallyindistinguishable from flesh-and-blood humans.

As it happens, all the townspeople seeking Mumford’s counsel are sexually and romanticallyblocked. The movie opens in a delightfully off-kilter way with a black-and-white 1950s-stylefilm-noir spoof that turns out to be the pulp-fiction fantasy of one of Mumford’s clients,Henry Follett (Pruitt Taylor Vince).

Follett is in despair that real life can never match his Barbara Stanwyck meets Frederick’s ofHollywood vision of down-and-dirty pleasure. Whenever the movie threatens to become tooserious, it dips back into Follett’s overheated fantasies for the sheer fun of it.

Follett, like everyone in the film, is a caricature. So is Althea Brockett (Mary McDonnell),the repressed, wound-too-tight wife of a loathsome investment banker and cigar aficionado(Ted Danson) who becomes Mumford’s client. Other local neurotics who end up on hiscouch include Nessa Watkins (Zooey Deschanel), a tortured, sarcastic, self-hating teen-agerwho lives in a dream world of fashion magazines, and Sofie Crisp (Hope Davis), adepressed young woman suffering from chronic fatigue syndrome.

As Sofie’s spirits revive on long walks that her therapist insists she take with him, theirmutual (and secret) romantic feelings for each other begin to bubble up.

With a sensibility rooted in psychotherapy and a major character who resembles a warmerand furrier Bill Gates, “Mumford” is right in step with the mood of the moment. So is itsall-American theme of self-invention in the computer age.

When Mumford and Skip swap life stories, the autobiography Mumford relates hasseemingly nothing to do with the bland, clean-cut young therapist who listens so attentivelyto other’s people’s problems. In his previous life, we learn, he was a ruthless investigatorfor the Internal Revenue Service and a cocaine addict who crashed and burned.

Mumford would be secure in his new life if he weren’t so good at his new trade. Histroubles begin when two local rivals, prodded by an irate, megalomaniacal lawyer (MartinShort), whom Mumford turned down as a client, begin an investigation into his past.

“Mumford” is at heart a Frank Capra-style social fable for the ’90s in which therapy (ratherthan civic duty or social conscience) is the catalyst that rouses people from their isolation andbrings them together, often in conveniently well-matched couples.

The movie also adds a running joke that pays off handsomely in having Mumford, who hasseceded from his former life, attracted to the television series “Unsolved Mysteries.” There’sa touch of science fiction in this “Zelig”-like character who is so unmarked by the depravityand desperation of his previous existence that he seems almost as freshly made as one of therobots in Skip’s secret laboratory.

There are moments when “Mumford” gets carried away with its vision of the therapist aseveryman, social healer and savior spreading sweetness and light. But there’s always that flyin the ointment. Mumford’s successful self-reinvention (not unlike that of certain crookedpoliticians who conveniently find Jesus) is suspect.