While Congress busies itself saving the bald eagle and the spotted owl, Cambridge is struggling to preserve its own particular endangered species: the mom and pop restaurant

Sure, the Square has its Au Bon Pain and its 31 Flavors. But all in all, Harvard Square prefers Elsie and Tommy to Wendy. It prefers Pinocchio's to Jack-in-the-Box.

Dwarfed by an institution that's three-and-a half centuries old, Square restaurants are bound to be a mere blip in the area's history.

But for each new crop of first years, three decades is enough to make a Square tradition seem as old as their red brick dormitories.

It's been about that long--nearly 32 years--since Joe Bartley bought a grocery store on Mass Ave. and turned it into a burger joint bearing his name.

"I felt there weren't any decent, large burgers around," says Bartley. "I gradually just tossed out the groceries and made it a legend."

Soon, after lobbying by the Bartley children, their mother, Joan, got official recognition; Mr. and Mrs. Bartley's Burger Cottage was born.

The Bartleys' decoration seems to follow no scheme. Customers are struck immediately by the eclectic assortment of historical relics and political memorabilia.

The Bartleys have, for example, the original sign for the now defunct Brattle Square T stop. Bumper stickers trumpet the campaign of Representative Joseph P. Kennedy II.

"Sweet Potato Fries Rich in Beta Carotene," announces one banner. "Please Don't Tamper With the Cook's Buns," says another. "Someone Else in '92," says a bumper sticker.

"I love humor," Joe says.

Inside, the sizzle of the trademark thick burgers blends with the shouting of orders to the cooks behind the counter. Hot grease pops on the grill.

At the booths and tables, graduate students discuss their courses over lime rickeys. Lone diners read newspapers or novels at the long table in the center of the room.

Dean of Students Archie C. Epps III, a regular at Bartley's, says he always finds interesting conversation there.

"[These are] people who ought to be teaching at Harvard," Epps says.

Dozens of blackboards proclaim, in colored chalk, the dizzying array of meals available at Bartley's. The menu itself is jammed with handwritten descriptions of pasta dishes, fried clams ("no bellies"), hot apple pan dowdy, cajun fried sweet potatoes, and of course, Mr. Bartley's celebrated burgers.

Bartley's began with a few standards burgers. Today, they offers about 20. To distinguish among them, the burgers often take the name of an appropriate celebrity.

Bartley says he tries to keep up with "who's in vogue."

The Madonna burger, for example, is "a naked burger stripped of its roll."

Bartley also gets political.

A few years ago, there was a Ronald Reagan burger served with a jelly bean. The Nancy Reagan Burger was served "on our best silver," says Bartley.

Current offerings include the George Bush burger ("not for the faint of heart") and the Bill Clinton burger ("don't inhale this slick burger").

Patrons can also sample various forms of potatoes (sweet, mashed and French fried) when they order "Dan Quayle's 'Poattoee' Trio."

Bartley is considering adding "Women's Club Sandwiches," which would be named after Tipper Gore, Hillary Clinton, Barbara Bush and Marilyn Quayle.

"People get a kick out of that," says Bartley, who has personally christened his burgers for 12 years. "Before people even eat, they start laughing. It puts them in a good frame of mind," he says.

Cambridge City Councillor Walter J. Sullivan is among a number of locals honored with a personalized burger. Featuring sauteed peppers and onions, the sandwich is "tasty," says Sullivan, who says health considerations prevent him from enjoying his namesake as often as he would like.

"It's a great sandwich," Sullivan says. He added, however, that he might go a little easier on the peppers.

The Bartleys have seen Harvard Square change quite a bit over the three decades they've spent on Mass Ave. "I've been the revolution of the 60s, the 70s, the 80s, the 90s," Joe says.

And though Joan says she kept a "family restaurant" even through the rebellious sixties, two darlings of the counterculture, Bob Dylan and Joan Baez, made Bartley's burgers a regular stop before of after folk performances.

Joan remembers one time when Baez and Dylan ordered nine Deluxes--"fries, the whole bit," she laughs.

The Bartleys' recollection of the two stars are vague--they were too busy running the business.

Besides, the Bartley's would lose a lot of time if they made star-gazing a common practice. Other famous dinners include Stephen King, Jackie Kennedy, Ted Koppel, Jimmy Breslin and Norman Mailer '43.

Joe figures that his restaurant has always drawn an eclectic crowd--like Dylan, Baez and other countercultural figures--because of its unusual atmosphere.

"I think it was the informality of the whole thing," he says. "It was like their home. You didn't have to be dressed to the hilt."

"Then, they took to me and Mrs. Bartley like pa and ma away from home."

Joe says that sort of feeling is harder to come by these days with a Square that is busier, more developed and more commercial.

"People in general are more hurried." Joan agrees. "There's probably more of a rushed feeling to the Square. It used to be more of a student's Square," she says.

"[Harvard Square] needs to retain something of its old character," Epps says, "and Bartley's is one of the few places which represents that now."

The Cambridge City Council--with its restrictions on franchises--is on the side of places like Bartley's, even as McDonald's slips under the iron curtain into Russia and Eastern Europe.

And that is a large source of comfort for Joe and Joan Bartley.

"I'll sound like sour grapes, but I think that's what has kept the Square different," Joe says. If franchises ever found their way into Harvard Square, he says, "it'd get to be a neon jungle."

In this presidential campaign season, words like change and reform have taken on a sort of mystical quality for disenchanted voters. But in Joe Bartley's world of burgers, rings and regular customers, the status quo seems just fine.

"I had a fella in here Saturday," Bartley says of a first time customer. "He said, 'Never franchise this place.' I said, 'I won't.'''

And Joe Bartley likes to tell of a Zaggart restaurant review. His favorite line. "I hope the place never changes."

"I think that's been the secret--it hasn't changed," Joe says. "It's kept its identity that people have liked over the years.

"Kids will come in here and put their feet up on the chair. That's been the secret--it never went high fallutin;"

Almost as varied as Bartley's ultra-diversified menu is its clientele. "I get all types--students, businessmen, older people," says Joe Bartley. "We get the melting pot, that's what's fascinating about it."

Tourists, too, know of the Harvard Square legend. "I get people in here from Montana who'll take onion rings home with them," Joe says.

Bartley's regulars include Harvard faculty members and administrators. Epps, Joan Bartley says, "has been around from when we first put in tables."

"They seem to be able to produce my favorite sandwich," Epps says, "which is the bacon cheeseburger: very well done--burned--heavy on the pickles."

Students also see Bartleys' as an endangered species.

"It's one of the few things in the Square that hasn't become completely generic--this and Elise's," says Steven D. Nelson, a second year graduate student in fine arts.

Although students inevitably graduate and move on, Joe says, they often come back.

"People return who graduated more than 25 years ago, with their kids. I always get a real kick out of that," he says.

Diners leaving Bartley's, pass a sign over the doorway which says, "Thank You/31 Years."

Come February, it'll be thirty two years. And counting.