Reston's brand-new downtown was blacked out yesterday, when a power company contractor digging nearby sliced through an electrical cable.

The lights went out at the 85-acre Reston Town Center, the planned community's office and retail complex that was years in the making, about 11:25 a.m. Power was restored around 5:40 p.m.

The outage left some 3,000 Virginia Power customers outside the center without electricity for about an hour. Several businesses along Baron Cameron Avenue (Route 606), the main street linking Herndon and Reston, were affected, including some restaurants that had to close at lunchtime. Traffic was snarled because signal lights were out.

Most retail stores in the glittering three-week-old Town Center complex had to lock their doors on customers coming to shop on Veterans Day.

"All day long, customers with little kids were knocking on the door," said Margaret Curran, a manager of Gapkids, which closed because without power the store could not use its cash registers or verify credit card purchases. "People were ready to buy and the store is dark."

Curran said the store had prepared for heavy business because of the federal holiday, but instead was turning customers away. Employees were left unpacking boxes by sunlight and, later in the day, by flashlight.

Gilbert Dawson, a shift supervisor at Virginia Power, said company contractors were digging with backhoes when an underground cable was struck. Dawson could not explain why the cable was cut or whether it was marked.

"It's pretty unusual for one of our contractors to cut our cables because our cables are usually marked," Dawson said. "All of that will be looked into tomorrow."

In the meantime, Town Center workers were faced with doing business without modern conveniences.

John Tyers, marketing director for the center, said the 514-room Hyatt Regency Reston hotel shuffled meetings and received help with food service from other nearby Hyatt hotels.

One elevator running on a back-up power supply carried workers up and down the 11-story tower that houses Reston Town Center Associates, the center's developer. Without facsimile machines, electric typewriters and word processors, employees continued working to lease the rest of the 220,000 square feet of retail space in the complex. About 40 percent has been leased.

"Some of us worked right through . . . to keep this moving," said Hunter Richardson, development manager. "It makes all our lives a little more difficult. We have deadlines to meet and we're trying to get this retail space filled."