D.C. Mayor Anthony A. Williams, pelleted by angry complaints that telecommunications companies have been carving up city streets, declared two weeks ago that the firms would complete their downtown work by Thanksgiving.

But a ride through downtown yesterday showed a handful of streets where work has not been finished--stretches where the contractor has left a strip of exposed concrete and has not completed the job with top layer of asphalt.

At one of downtown's busiest intersections, 12th and G streets NW, work crews were knee-high in a trench being dug on 12th Street near the entrance to the Metro Center subway station.

From 12th to 11th streets along G Street, large sections of asphalt were missing, making the roadway look like a jigsaw puzzle and challenging motorists and cyclists. From 10th to 11th streets, half a lane was covered with asphalt and half was exposed concrete base, about two inches lower.

Along K Street NW, a major downtown thoroughfare, a ribbon of exposed concrete base runs from 19th to 21st streets.

City officials said the unfinished work will stay that way until after Jan. 3, because the District is imposing a six-week moratorium on downtown street construction between Thanksgiving and the New Year's Day. The holiday season moratorium, an annual practice in recent years, is designed to make the downtown streets hospitable to shoppers, Lawson said.

Art Lawson, deputy director of public works, said contractors who could not finish their downtown work will not be penalized. He said they will finish the work after Jan. 3.

"The goal was to have them finish as much as possible," Lawson said. "Because of the number of cuts out there and the sheer number of temporary repairs that had to go to permanent, they just didn't get them all done. We will make sure they are left in a safe and passable condition. Then they will come back in and make the permanent repairs after the moratorium."

The telecommunications companies, which are racing to lay fiber-optic cable beneath city streets for high-speed Internet, cable television and telephone service, have dug trenches through a large portion of downtown streets, ripping away asphalt and leaving motorists to navigate uneven roads, potholes and jagged metal planks.

Lack of coordination has caused companies to attack the same street in succession, so that a road is sliced open, patched up and then cut open again with the next work crew. City officials announced this month new efforts to improve timing of the road work and exert greater control over the construction schedule.

To install pipe or wire, utility companies typically break through a two-inch layer of asphalt and about 10 inches of concrete until they reach soil. They bury the conduit, then backfill the trench with dirt and put a thin layer of asphalt on top. That is considered a temporary patch, which is often rough and bumpy.

Later, the company hires a construction firm to dig up the temporary patch, fill it with concrete and cover it with a permanent asphalt top.

On the downtown streets where companies left a ribbon of exposed concrete base, they must return to lay the permanent asphalt top for a repair to be considered complete.

To date, the District has not made the companies pay for the right to use underground space--fees that are levied by several other cities. But Lawson said yesterday that the District is planning to initiate fees early next year. He said that the District has met twice with utility companies to discuss prices and that the city expects to propose a fee schedule early next month.

In all, nine telecommunications companies hold about 145 permits to lay pipe and fiber-optic cable beneath city streets, city officials said. More than half that work is completed but the city expects more requests for permits.

After the downtown moratorium on street work ends Jan. 3, Lawson said, contractors are likely to be back on the streets, digging new trenches. He said he did not know how many companies hold permits to begin work in January.

CAPTION: Pedestrians cross 12th Street NW at one of the construction sites that was ordered to be completed by yesterday.