Transportation officials in the Washington area sent out alerts across the East Coast yesterday advising drivers to avoid the eastern arc of the Capital Beltway tomorrow evening when former president Ronald Reagan's coffin is taken from Andrews Air Force Base to the Capitol.

It was one of many warnings to travelers in the hopes of avoiding three days of gridlock in the region.

Officials also asked people to use mass transit tomorrow through Friday, try to leave work early tomorrow and even take time off, if possible.

Traffic problems are likely throughout the ceremonial period. Tomorrow's evening rush hour may be the worst as the coffin is moved at 6 p.m. from Andrews into the District. It will be transferred from a hearse to a horse-drawn caisson for a procession that is to start near 16th Street and Constitution Avenue NW, head down Pennsylvania Avenue and arrive at the Capitol about 6:50 p.m.

District officials yesterday did not have a complete report of road closures, but they said that Constitution Avenue from 17th Street past the Capitol probably would be closed tomorrow from about 5:30 to 8:30 p.m. Parts of Independence Avenue near the Capitol also are likely to be closed during that time.

Parking will be prohibited on Constitution Avenue NW between 17th Street NW and First Street NE from 3 p.m. today to midnight tomorrow, District transportation officials said. Cars will not be able to cross that stretch of Constitution for blocks of time between 2 and 9 p.m. tomorrow. Drivers can get updated information on the radio by tuning to 1630 AM.

The route through the suburbs has not been disclosed, but Maryland officials said they expect significant traffic tie-ups on major and secondary roads. They advise drivers to circle around the western half of the Beltway or follow Route 301.

Should the motorcade take a route that includes the Beltway, that highway would be closed for an hour or more, a situation that transportation officials said would cause traffic reverberations across the region.

Inner loop drivers could sit for hours as the road is cleared for the Reagan motorcade. Outer loop drivers almost certainly would be stuck in bumper-to-bumper congestion as drivers slow for a look at the motorcade. Secondary roads would be crammed with people trying for alternative routes, and motorists trying to avoid the Andrews area by heading around the other side of the Beltway would overwhelm already strained roads in Montgomery County and Virginia.

"People will have to expect major delays for several hours Wednesday night," said David Buck, a spokesman for the Maryland State Highway Administration, who struggled to think of a comparable traffic event.

Buck said traffic operations would be at the high level of staffing they were for the millennium New Year's celebration and other major events and would include extra operations and maintenance personnel.

On Thursday, transportation officials expect tens of thousands of people to view Reagan's coffin at the Capitol. Even if all roads are open, officials are asking people to take Metrorail to the Capitol.

Metro officials said that several bus routes would be affected by road closures. Because Friday has been declared a federal holiday, MetroAccess customers must call to schedule regular trips. Metrorail will operate on its normal weekday schedule all week, including Friday, officials said.

On Friday, Reagan's coffin will be taken from the Capitol to Washington National Cathedral at 10:30 a.m. for the funeral service. Afterward, at 1:15 p.m., the coffin will be taken to Andrews. Officials said they don't have the details of that day's route, but they noted that there is no easy way to get from Wisconsin Avenue NW to Andrews. The motorcade will either have to twist back through the city or head north to the Beltway and follow it for several miles, interrupting trips for midday drivers.

Virginia officials said they are debating whether to lift HOV restrictions Friday, the federal holiday.

There are not many things Washington area drivers will accept as legitimate reasons for slowing their drive times, but transportation officials are hoping that this occasion will be one of them.

"We are the capital of the United States," said Lon Anderson, spokesman for AAA Mid-Atlantic. "While it will certainly slow up traffic for those out there, regionally we're very good at making adjustments [for] these kinds of special events."

Buck begged drivers for a little patience.

"We have one of the most popular presidents of the 20th century" in Reagan, he said. "I hope people are willing to put up with an afternoon's worth of bad traffic out of respect for what's happening."