A massive storm centered in the nation's midsection was expected to bring sleet and freezing rain to the Washington region today, a messy mixture that could turn to ice in some suburban areas as temperatures drop tonight, forecasters said.

The outer edges of the storm were to hit Washington about 6 a.m., with a few snowflakes joining the sleet and freezing rain, said Brian Lasorsa, a meteorologist with the National Weather Service. The precipitation will probably continue all day and eventually turn to rain in and around the District as temperatures hover just above freezing.

The freezing rain or drizzle was expected to persist in areas to the north and west, such as Loudoun County and western Montgomery County. Those areas could have ice and power outages, making tomorrow morning's rush especially troublesome if roads are not treated properly, Lasorsa said.

"Our primary concern is ice accumulation from freezing rain," he said. "That is definitely the number one problem this storm presents."

But the area is likely to be spared the wintry blast of the recent Valentine's Day storm that closed schools and airports and clogged roads with snow, sleet, ice and slush. "This will not be like the last event, where temperatures just plummeted and ice just froze rock solid and nothing could be done," Lasorsa said. "As far as it being a solid sheet of ice that can't be treated at all, we shouldn't be dealing with that."

Nevertheless, in a discussion of its predictions, issued shortly after 9 p.m., the Weather Service called the forecast "challenging," describing the storm as a "complex event." It said it was not yet possible to tell how much and what kind of precipitation would fall where.

Road crews were ramping up a vigorous response. Virginia's Department of Transportation planned to deploy 500 salt trucks throughout Northern Virginia by 6 a.m. "Based on last week's storm, we want to be on top of it as early as possible,'' said Joan Morris, a VDOT spokeswoman. "Sunday night would be the worry, if the temperatures hover around 32 degrees and then drop at night."

Maryland officials prepared to deploy at least 1,000 people, including state crews and private contractors, to operate salt trucks around the Washington-Baltimore region, said Valerie Edgar, of the State Highway Administration. "We're keeping an eye on it, and we're ready,'' she said. "It's not like it's going to be a surprise. ... And it will be a Sunday, so we won't have to contend with rush hour."

The District planned to begin treating main roads, bridges and overpasses with salt and brine last night, said Karyn LeBlanc of the Department of Transportation, and deploy the city's 150 salt trucks early today.

City transportation officials received a mixed review last week for their Valentine's Day storm performance. Despite the dispatch of hundreds of trucks and snow-removal workers, many primary and secondary roads were left untreated into the late morning and early afternoon. The stubborn coat of ice also remained on many suburban streets for days.

Staff writers Keith L. Alexander and Martin Weil contributed to this report.