Thousands of travelers who streamed out of Washington yesterday to begin the the first long weekend of the warm-weather season found the traditional delays at the traditional traffic bottlenecks, but encountered few unexpected tieups elsewhere.

Despite yesterday's clear skies that enhanced the appeal of the shore and helped to smooth the way for motorists, the National Weather Service warned that showers are possible today and tomorrow at the beach as well as in the Washington area.

A cold front is expected to keep temperatures in the 70s and below normal, and at beach resorts from Delaware north, forecasts indicate the water will be chilly: below the 60 degree mark.

Motorists found yesterday's principal backups and slowdowns at such places as the Baltimore Harbor Tunnel and the Chesapeake Bay Bridge.

At times, lines of vehicles waiting to enter the harbor tunnel stretched for three miles southbound and for two miles in the opposite direction.

While use of the tunnel was heavy, and was expected to remain so through the weekend, said Arnold Street, a tunnel police officer, the overall level of traffic there seemed "just a little bit more" than on an average Friday.

At the bay bridge, a principal link between Washington and the Eastern Shore and the ocean beaches, shorebound vehicles waiting to enter the toll plaza were lined up for two to three miles, bay bridge and state police said last night.

Traffic across the bridge was described by an officer there as "real heavy" and "moving pretty slow."

Between 5 p.m. and 6 p.m., 2,451 vehicles crossed the bridge eastbound and 1,099 westbound.

A State Police dispatcher in Anne Arundel County, on the west side of the bridge, pointed out that the congestion was typical of a major holiday weekend.

"It's usually like this on any three-day weekend that's a nice weekend," the dispatcher said.

Closer to Washington, a major delay cropped up at the link between the George Washington Memorial Parkway and the portion of the Capital Beltway that leads across the Cabin John Bridge into Maryland.

At one time, according to a Maryland State Police report, the backup there was estimated at eight miles. No reason other than heavy traffic was cited by any of the police departments with jurisdiction.

Virginia State Police in Fairfax County reported that evening rush hour traffic was heavy and slow-moving. No major delays or accidents were reported elsewhere in the area, and an officer in the D.C. police traffic unit reported that in contrast to the normal holiday weekend custom, "everything seems to be running fairly smoothly."

Early departures appeared to be one possible cause. A spokesman for the federal Office of Personnel Management said that while no figures were available, he suspected that "quite a lot of people took off" yesterday.

They "evidently did," observed a Virginia State Police dispatcher who reported that traffic on typically clogged Interstate Rte. 95 in Northern Virginia appeared to be flowing smoothly in the early evening.

At Baltimore-Washington International Airport, for example, police said Thursday night's traffic appeared heavier than last night's.

Last night's activity was "a little bit more than usual," said Darrell Robertson, a state police sergeant posted at the airport. But, he added, "several people commented that Thursday night looked like Christmas."

At National Airport, on the other hand, extremely heavy car and pedestrian traffic in and around the terminal was reported last night.

Amtrak said it put extra cars on at least two of its trains in the New York-Washington corridor yesterday, but still had a few standees in them.

Extra Trailways buses were also being put into service last night, said terminal supervisor William A. Penn, who reported the bus station about three times as busy yesterday as on a normal Friday. Penn said many travelers appeared headed south toward North Carolina.

Greyhound assistant district manager Marvin Prince said he expected the heaviest ridership of the weekend between 6 p.m. last night and noon today.

This prediction appeared to conform to that given by Charles Ebersberger, who from his sporting goods store on Rte. 50, about 2 1/2 miles west of the bay bridge, has long observed shorebound traffic. After considering last night's line of cars, he told a reporter: "It'll get worse."

At least one major bottleneck of yore is expected to be relieved, however. In the past the Kent Narrows drawbridge, five miles east of the bay bridge has been opened for the passage of boats every daytime hour on the hour.

Now, officials say, it will be opened only at intervals, with raisings today at 6 a.m., 9 a.m., noon and on the hour from 3 to 8 p.m.

Sunday and Memorial Day raisings will be on the hour from 6 a.m. to 1 p.m. and again at 8 p.m.