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.