LIKE A PAIR of Levi's Action Slacks, Albert Brooks' romantic comedy "Lost in America" is tailor-made for baby- boomers pushing middle age.

The film's characters look to '60s cult films for inspiration; the self-mocking humor and sight gags are right out of "Saturday Night Live" (which aired Brooks' first films); and there's a climactic sell-out that mirrors the materialism of many former flower children.

As director, co-writer and star of "Lost in America," Brooks has created a fine vehicle with which to strut his comic strengths. Whether expressing joy, fury or horror, he always seems on the verge of going a tad too far, and we eagerly await the moment when his respectable-looking character will cross the line into uncontrolled dementia. Even the other actors in the film seem a little wary of Brooks' rantings (look for their side glances), which further accentuates the comic unpredictability.

The film begins with Yuppie couple Linda (Julie Hagerty) and David (Brooks) spouting cliches about growing stodgy: "Nothing is changing anymore. Life is passing us by." He's a successful ad executive, she's a personnel director at a tony department store. He wants a boat and a Mercedes, she wants more excitement.

When David is turned down for a promotion, however, hell breaks loose -- in one marvelous scene he warns a jingle-spouting ad man, "Your songs stink; I hate your suit; and I could hurt you, Brad!" David curses his Nerf-Ball- squeezing boss, gets fired, and sets out to recreate the mythic voyages of the '60s: "My wife and I have dropped out of society. We're going to roam the country finding ourselves, just like in 'Easy Rider.' "

Hagerty and Brooks make a lovely duo as they drive across America. There is something oddly endearing about the fallen Yuppies' Winnebago cruising along to the rock classic "Born to Be Wild." And when David takes a job as a crossing-guard ("I'm warning you, kid, walk your bike!"), we are treated to a sad little scene where the man realizes that his dreams may have been foolhardy.

"Lost in America" is a winner -- chock full of subtle cameo performances (Garry Marshall is superb as a businesslike casino manager), big yuks and the occasional bit of pathos. Brooks appears to have fulfilled his long-heralded potential for film-making with this state- of-the-art romantic comedy. LOST IN AMERICA (R) -- At the KB Cerberus and Tenley Circle.