SOMERVILLE — Three young caffeine merchants with an attitude are prospering in Davis Square, and just as they arrived ahead of the coffee wave out of the Pacific Northwest, they appear to be slightly ahead of other developments that could bring a renewed vigor to the square.

On Tuesday, their landlord will publicly announce plans to add four theaters to the Hobbs Building, already home to the Somerville Theater, and next month, the first phase of an Asian-theme mall is to open next door.

But the owners of the Someday Cafe — Jeff Hale and Glen Wallace, both 25, and Steve Stevens, 27, all of Somerville — are expanding now, and out of necessity. Their combination of product and personality is not only making it hard to get a seat in their shop, but often produces a line from the service counter to the door.

Their formula for success is a simple one. "We wanted it to be kind of like coming into our living room with a really killer espresso machine, really good tunes, and, you know, tell us what you want," said Wallace, a friend of Hale's from Seattle who joined after four years as a disc jockey in Spokane.

It's no surprise, certainly, that a coffeehouse is succeeding in the '90s, what with Starbucks, Coffee Connection and the like. But here, the owners are striving for something different.

Just about everyone on their staff of about a dozen sports a tattoo or has pierced at least one body part. "The dirtier and holier you are, the better," Stevens said.

And emphatically, they don't wear uniforms. "We had an employee wearing his Someday Cafe T-shirt to work every day, and we had to have a little talk," Stevens said.

That the Someday strives to be the un-chain is evident even before you walk in. The sign on the door says, "Sorry, we're open," and a bumper sticker urges you to "Subvert the Dominant Paradigm." The irreverence shows up all over the cafe. On the cash register is a picture of a cellular phone, circled with a line through it, with the declaration, "Cellular Free Zone; We will not turn down the music for the excessively privileged."

"A lot of people are used to getting their butt smooched right inside the door, but we're making it by not doing it," Wallace said. "They might have a problem with the atmosphere, but not our product."

Indeed, the product -- including cappuccino, espresso, lattes, mochas, teas and flavored Italian sodas, plus scones and a caseful of other baked goods -- does seem to be popular, to the tune of about 500 cups a day, and 50 gallons of milk a week. But that's not all that brings customers in. "There's good people-watching here," said David Fagan, 29, who says he has been "checking out other cafes, but this is my first choice."

Ned Landin, 36, of Medford, is an artist who says he thinks the cafe is "a really cool place. "I like a lot of the music, the attitude of the people who work there, the art. They've really captured the idea of a coffeehouse."

The expansion, expected to be completed next month, will double the cafe's space. Some of the new seating will be on sofas and old chairs once used in the theater, and there'll be a performance area.

The three aren't certain what their next step will be, but they're already working on it. "We're saving our pennies so we can be obnoxious in more places. If this was it, we'd pay ourselves a lot more, and we could," Stevens said.

The Someday's success comes as no surprise to Melvin L. Fraiman, 70, who owns the Hobbs Building and operates the Somerville Theater within. In fact, he says it owes its success to the building. "The cafe is the tail wagging the dog. It's just one little entity," he said.

"Don't misunderstand me, they are a good tenant, but the building is the key. Imagine if {Someday} was across the street, what would it be then? Just another cafe."

Fraiman is so bullish on his building that he wants to add four new theaters on the Dover Street side. "So there is no confusion, we're not going to split the Somerville Theater," he said, hoping to allay concerns of those who value the building's rich history. "We have no intention of changing the character of the exterior or the interior of the Somerville Theater. That's very important."

Fraiman, a vigorous man who still plays squash several times a week, said he expects that neighbors' primary concern will be over traffic and parking, which already is difficult to find.

He spins out a formula that envisions the theaters bringing "only" 25 more cars to the square, and then only on busy Saturday nights, but it is contingent on filling only 400 seats, having 300 of those patrons arrive on the T, and having the other 100 arrive four to a car.

Patrick Reffett, city community development director, who says he is "absolutely" a supporter of the plan, also acknowledges that parking will be a key factor, and points out that the theaters' greatest need for parking will be at night, after some shops in the square have closed.

"Everybody recognizes it's a fairly prominent building in the square, and I think people realize it's better to have an active, productive use for it. It outweighs the negative," he said.

Fraiman said his plan includes large-scale refurbishing of the building, which has stood since 1912 and borders on being an eyesore. Bud Knox of the Chamber of Commerce calls it "deplorable," and Reffett says it has been "an absolute shambles for years." The front entrance is covered by a plywood door, and more than one window on the upper floors is broken.

Although the plans are drawn and the hearing has been scheduled, there is at least a little skepticism around the square that the project will ever be undertaken. For example, Stan Zafran, 36, who lives in Somerville and has operated his Yogurt Bar and Co. across the street from the theater building for five years, said he's been hearing rumors of such an expansion for six or seven years.

"I believe what I see. Not to be pessimistic, but to be realistic, that's a big undertaking," he said.

Fraiman, who also operates the Capitol Theater in Arlington, said he is confident that if he wins city approval for the project, he can get financing and begin work before the end of the year. He declined to say what his next move would be if he is denied permission, other than saying he would have to re-evaluate his options.

"What are we going to do, fix up a building that just sits there? You don't have to be a brain surgeon to figure that out," he said.