Repair costs from Tuesday's six-alarm fire in downtown Ellicott City could exceed $2 million, according to insurance agents surveying the damage yesterday. Close by, demolition crews began work on portions of the hardest-hit buildings.

Investigators in the Maryland fire marshal's office have ruled out arson and expect to identify the fire's cause early next week.

The downtown's central artery, Main Street, reopened yesterday morning as did all the undamaged businesses. Cheery shopkeepers chatted with longtime customers, bemoaning the fire but expressing optimism that shoppers would return en masse for the crucial Christmas season. The quick turnaround surprised even the city's most ardent boosters.

"After the fire in 1984, it took four or five days for anything to happen," said Linda Fisher, owner of Fisher's Bakery, which burned down in 1984 and was rebuilt. The shop was not damaged Tuesday.

Fisher and some other merchants praised Howard County Executive James N. Robey (R) for quickly pressing county agencies into action after the fire broke out. Robey was on the scene Tuesday, just minutes after firefighters, and stayed well into the night. The next day, he met privately with store owners to hear their concerns.

"He's not just talk. He's about action," Fisher said.

The estimated cost of rebuilding crept up yesterday, to $2 million, as insurance agents realized that the narrow design of Main Street will hamper construction and that the stringent aesthetic regulations governing the historic zone will involve costs not incurred by typical building projects.

The fronts of the damaged stores are feet from Main Street; in the rear, where most of the damage is, the buildings are backed up against a hill. The situation precludes the use of heavy construction equipment, insurance agents said. Much of the rebuilding will have to be done by hand, which increases labor costs, they said.

Yesterday, barricades blocked the charred storefronts from view. Workers in hard hats buzzed about, measuring beams, hauling away debris. The smell of smoke, so dominant for two days, competed with that of fresh lumber.

Caplan's Antiques, next to the stretch of seven damaged buildings, was open for business. None of the dozens of Tiffany lamps or mahogany shelves inside had a scratch. The owners, Shelley and John Caplan, had been more concerned about their beloved Persian cat, Ashley, who was missing until yesterday morning.

"I walked in this morning and called out her name. She came out from underneath some furniture. She was fine. A little hungry, but fine," said store clerk Sue Graham, as Ashley slept on a couch nearby.