A four-alarm fire raced through a three-story wood building in Harvard Square early yesterday morning, injuring three firefighters and causing extensive damage to the four businesses in the building.

The injured firefighters were treated for minor injuries and were released at the scene of the fire, Cambridge's Deputy Fire Chief Edward Dodley said yesterday. Dudley estimated up to $100,000 in damage to the four businesses located in the 14 Eliot St. building.

Seventy firefighters battle for over three hours to halt the blaze, which was started by a faulty oil heating system in the basement, Dudley said.

"It looked like a bomb went off in there [the building]," said Kieran Brennan, a private contractor working for the Robert Banker Real Estate firm.

The two stores in the basement. The Vintage Restaurant and A Wine For All Reasons, suffered the most substantial property losses. Cambridge Patrolman James Scott said last night. Banker Real Estate and Clivus Multrum, a manufacturer of waterless toilets, incurred smaller, but also significant, damages.

But building owner Robert Banker '58 said the building sustained minimal structural damage, adding that he hoped the building would be "restored much to its original form" in four weeks.

In an unrelated incident, a small fire broke out in the basement of the Varsity Liquor Store early yesterday afternoon, but was quickly squelched by the Cambridge Fire Department.

There were no injuries and damages were estimated at $75, according to store worker Thomas Tryon.