With construction workers poised to break ground on four local projects--Read Block, Winthrop Park, Zero Arrow Street and the Coop Annex Building--it looks like it's hip to be in the Square.

Developers appear confident the economy here is booming. But real estate development has some longtime Square watchers concerned about the future of New England's second-most popular tourist attraction.

Will large-scale development kill the vitality, diversity and uniqueness of the Square--"the goose that lays the golden eggs?" as City Councillor Francis Duehay and the membership of the Harvard Square Defense Fund (HSDF) likes to call the area.

G. Pebble Gifford, president of the HSDF, has spent decades worrying about--and fighting over if necessary--the Square's future. Development threatens the Square's charm by increasing traffic, building density and rent, not to mention the structures themselves.

In all four of the imminent projects, maintaining the Square's aesthetics has been a key concern of developers, in part because HSDF and the Cambridge Historical Commission (CHC) have made it one.

The architects for Winthrop Square and Read Block drafted several scaled-down versions of their original plans before placating the cries of protectionists--cries backed up by city law.

As the city of Cambridge's protectionist arm, the CHC shields historic properties from "inappropriate" development and uses its demolition permits and landmarking powers as bargaining chips during negotiations.

When Cambridge Savings Bank originally proposed to tear down Read Block in 1994, the CHC began a landmark study on the three properties in the center of Harvard Square, a process which prevented all construction work on the buildings and threatened its future development.

Three years later, the Bank agreed to completely restore--rather than raze--the buildings.

Despite such guardianship, there have been some Square developments that have failed to meet preservationists' standards. HSDF Vice President John R. Moot '43 points to the HMV building and the Charles Hotel as dis- appointments.

Cambridge is now exploring both the possibility of rezoning and designating the Square a historical district to further curb projects that jeopardize historical integrity.

Yet the city has little control over tenancy, meaning the Winthrop Park development could feature the Square's third CVS if an entrepreneur was eager enough.

And it's the threat of the "chain creep"--the proliferation of brand-name superstores--that elicits much aggression from the Defense Fund.

Gifford argues that visitors flock to the Square for its unique charm, and not for stores one could find in Anymall, USA.

"No one's going to come to Harvard Square for a Dunkin' Donuts," Gifford said.

What does draw people to the area, says Gifford, are long-standing, "idiosyncratic" establishments like The Tasty and Grendel's Den Restaurant.