Not that Joe Sears and Jaston Williams play only the distaff side in their popular Tuna comedies. An essential appeal of the shows - including the third and newest, ``Red , White and Tuna ,'' which premieres tonight at Galveston's Grand 1894 Opera House - is that the pair portray all the wacky denizens of the mythic "third-smallest town in Texas." Young or old, male or female, nutty or . . . well, let's face it, they're all a bit nutty, Sears and Williams bring them to colorful life.

Yet it's Tuna 's womenfolk, such as Williams' prissy busybody Vera Carp and Sears' homey Aunt Pearl (that's "homey," not "homely"), who usually prove the funniest and most memorable.

Meeting the Tuna guys backstage at the Grand, dressed in their civvies and minus those daintily chintzy discount-store frocks, Sears and Williams could be part of the stage crew.

But don't let appearances fool you. From the time ``Greater Tuna '' premiered in Austin in 1981, through its extensive tours and yearlong off-Broadway run, through ``Tuna Christmas' '' 1989 premiere in San Francisco, its many tours and acclaimed Broadway run, Sears and Williams have established themselves as two of this country's most versatile character actors.

No surprise that they were both born actors - Williams in Crosbyton, Texas, and Sears in Bartlesville, Okla., (and transplanted to Texas in the early 1970s). As kids, they both liked putting on costumes and becoming someone else.

"At age 4," says Williams, "I was a Wise Man in a Nativity pageant. I got in a fight with the two other Wise Men."

"I was a costume nut from the start," says Sears. "My first time onstage in a school play, I was a Roman whipping Jesus. I really got into it, loved the costume. The next time, I was one of the Wise Men - I got to wear a cape!"

By high school, Sears had his first speaking role in a Shakespeare play, while the adolescent Williams became fascinated with Eugene Ionesco and other avant-garde playwrights.

"It makes us a natural complement as a team," said Sears, "that Jaston is interested in the avant-garde and I'm more of a traditionalist."

They first worked together in a production of Shakespeare's ``A Midsummer Night's Dream'' in 1973 at San Antonio's First Repertory Company. As they became friends, they collaborated on other projects, both as actors and producers - everything from Chekhov's ``The Three Sisters'' to Bruce Jay Friedman's ``Steambath'' to old-time melodramas. Like most actors, they have held other jobs along the way: Sears as a bartender and a teacher, Williams spending five years as "the worst waiter ever."

By the late '70s, seeking something new they could perform together, they began developing ``Greater Tuna .''

"We wanted something that would comment on the political scene," said Williams. "A political cartoon was what we were thinking of - a caricature, but with real acting and real issues. We've tried to keep that balance in the other shows as we got older - though they've become more real and less caricature. I think that's because, as you get older, you discover that what was thought of as caricature actually is reality."

The team had ``Red , White and Tuna '' working "in their heads" for two or three years, then spent last summer getting it down on paper. They tried out the new material in a workshop at a small Dallas venue this past fall.

"The first show was about politics," said Williams. "The second was about relationships. This one is about change. We see how the characters have changed. We couldn't have written this one when we did the first show. A lot of what it deals with just comes with the passage of time and living through certain things. We're taking on divorce, death, aging and the classic baby boomer situation that we're all getting to now - where we find we're becoming the caregivers for elderly parents. That's scary, but there are many aspects that are funny."

Williams recalled a recent incident with his mother, when he found her driving with the rearview mirror turned to the floor. Her explanation: "It just throws me off!" That line got into ``Red , White and Tuna ,'' where it's spoken by Aunt Pearl, who also is "getting up there" in years.

Along with old favorites, the new show introduces some new characters, including two aging but still mellow hippie chicks, who return to Tuna for a high school reunion. Sears and Williams admit to getting a special kick out of the new creations, Amber Wind-Chime and Star Bird-Feather.

The show is set on the Fourth of July, and the creators promise some "little satiric digs" about the Tuna -ites' attitudes toward God and country. For instance: Vera and her "Smut Snatchers" have taken to rewriting hymns with objectionable lyrics.

They also note that a second-act sequence at the high school reunion gives them one of their busiest quick-changing, multiple-character sequences yet.

Sears and Williams prefer to try out a new show close to their Austin base, in a city they consider a "Tuna stronghold." They take into account both audience and critical reaction as they develop a new piece.

"We like to have our fans here be the ones to tell us what's not working," said Sears. "That gives the backbone, the strength to improve it." The new show will go on to dates in Austin, San Antonio, Fort Worth, probably coming to Houston in late summer. Next year, they will take the show on a wider tour, including San Francisco, Seattle and Washington, D.C.

Though firmly established as a performing team, Sears and Williams do occasional independent projects. They also have worked together on non-Tuna shows, including Larry Shue's ``The Foreigner'' and a special production of ``The Fantasticks'' at Ford's Theater in Washington, D.C. It was revised by the show's creators, Tom Jones and Harvey Schmidt, so that Sears and Williams could play the Fathers, as well as the Old Actor and the Indian. More costume changes.

Representing the classic visual contrast of the great comedy teams - one portly, one slight - Sears and Williams could be considered a Texas-inflected Laurel and Hardy.

"We definitely think of ourselves as a team when we're doing the Tuna projects," said Sears. "We've worked together longer than most comedy teams."

There is a third member of the ``Tuna '' team: Ed Howard, who co-writes and directs the shows (but unlike Sears and Williams, never appears onstage).

Sears and Williams are pretty sure that ``Red , White and Tuna '' will complete their "Tuna Trilogy."

"But we've learned to never say never," says Sears. "A lot of people have suggested we do a ``Tuna '' show set at Halloween. And that would be funny."

Imagine the possibilities: costumes upon costumes. How can the ``Tuna '' guys resist?