A crucial delay in salting and sanding city streets helped turn the District's main commuter thoroughfares into slippery sheets of ice yesterday, and getting to work became, for thousands of commuters, the most trying challenge of the day.

Despite early forecasts of sleet and snow, the D.C. Department of Public Works waited several hours before mobilizing its road crews, and by rush hour many major roads -- including Wisconsin and Connecticut avenues and Rte. I-295 -- were virtually paralyzed.

Commuters, waiting for buses stranded in traffic, began knocking on the windows of cars stopped at lights, begging for rides.

Before long, automobiles resembled the Manhattan subway at rush hour: No seats and no standing room.

Metro transit officials added 73 trains for the morning commute. But for some of those taking buses, as well as for some suburbanites who traveled into the District by car, a trip that normally took 30 minutes stretched to a frustrating three hours.

Road conditions let up slightly during the day, but streets remained slippery through last night because of freezing temperatures.

Forecasters had begun predicting snow and ice as early as Thursday morning. Light sleet and freezing rain started falling as early as 9 p.m. in some areas, and limited crews began salting bridges going into the District at midnight, said Anne Hoey, a city Public Works official.

At 3 a.m., about 30 salt trucks were at work, but it was not until 6 a.m. that the full complement of 81 trucks was mobilized, Hoey said.

By contrast, highway crews in outlying areas were apparently better prepared for the ice storm. For example, Maryland highway officials had 425 pieces of equipment plowing and salting roads in metropolitan areas early yesterday and through the rush hour, a spokesman said.

Public Works officials in the District said they decided how many works crews to alert and when to deploy them based on their surveillance of street conditions and on weather forecasts that, they contend, indicated temperatures would be above freezing by the time rush hour began.

"The forecast we were getting even at 9 p.m. (Thursday) was that the temperature was going to stay above freezing or that the ice did not stick to the streets," said George Schoene, chief of the department's Bureau of Traffic Services.

"When we realized that the prediction was wrong, we started mobilizing, and I think that some of the main roads were already frozen over," he said. "By that time it was a little late as far as traffic was concerned . . . .

"Remember the storm about two weeks ago?" Schoene asked, when reminded of the day's previous forecasts and the early start of the precipitation. "They predicted eight inches and we got about one inch. Sometimes the forecasters are wrong."

But an official at one of the weather services that provides information to the department said his agency had issued its "highest level of winter storm warning" at 12:30 a.m. yesterday.

"That warning is our call to action," said Joel Myers, president of Accu-Weather Inc., a private weather service in State College, Pa. "I'm hearing that the department is saying the storm took them by surprise, and if that's the case, we beg to differ," Myers said. "We don't want to criticize a client, but we were predicting 29 degrees for 6 a.m. -- it was actually 27 -- and a strong northeast wind that would make it even colder."

The sleet, snow and freezing rain were the result of a low-pressure system that passed across the Washington metropolitan area on its way up the coast to New England. While Dulles International Airport recorded an inch of precipitation, both National and Baltimore-Washington International airports reported only .03 of an inch.

Yesterday's high here was 32 degrees. Partial clearing is expected today, with the high in the 40s.

For most Washington workers, getting to work yesterday was a study in frustration.

Rhonda Franklin, a receptionist at the National Kidney Foundation, left her home on Xenia Street SE at 7 a.m. Taking a bus, she got to the foundation's office at 2233 Wisconsin Ave. NW 3 1/2 hours later. She was, it turned out, among the first to arrive.

"I found the whole thing particularly frustrating," Franklin said. "On top of everything else, I'm eight months pregnant.