From John Matthews' vantage point, there is one foolproof way of driving to the beach on the July 4 weekend without getting tangled in a traffic tie-up: Start out before sunrise.

Matthews, a veteran police lieutenant, is no stranger to holiday road jams. His command post is at the Chesapeake Bay Bridge, the frequently backed-up gateway to the Maryland and Delaware coast. "If I was going, I would be here paying my toll by 6 o'clock Saturday morning," Matthews said.

According to Matthews and regional highway officials, the Bay Bridge is likely, at least during less auspicious hours, to prove one of the biggest bottlenecks of the July 4 weekend, a holiday expected to snarl traffic in the District of Columbia as well as on key routes to ocean beaches.

In the District, most disruption is predicted for Monday, when Independence Day parades, demonstrations and fireworks displays will lead to temporary street closings. The Metro transit authority and Montgomery County's Ride-On bus system plan to provide special July 4 service to ease the crush.

For weekend beachgoers, traffic slowdowns and backups are predicted on key crossings including the Kent Narrows drawbridge on Maryland's Eastern Shore and the Hampton Roads bridge-tunnel leading toward Virginia Beach. Traffic is expected to be especially heavy this afternoon and evening, tomorrow morning and Monday afternoon and evening.

In addition to Matthews' suggestion that travelers start out before sunrise, highway officials recommended several other ways to avoid the stickiest traffic jams. They urge drivers either to begin their weekend trips this morning or to wait until late this evening, and suggest returning either early Monday or waiting until Tuesday morning.

"I would expect the heaviest traffic would be Monday night. Almost everybody's got to be at work Tuesday," said Edward H. Meehan, acting highway engineer for suburban Maryland.

In the District, traffic will be impeded on several thoroughfares because of construction projects. These roads include 16th Street NW between Emerson and Kennedy streets, where only one lane is open in each direction. Pennsylvania Avenue NW has been temporarily narrowed between Third and 10th streets, as has the New York Avenue bridge over the Anacostia River in Northeast.

In Northern Virginia and suburban Maryland, highway officials said that all work will be halted during the weekend on major constuction projects in an effort to prevent tie-ups. Capital Beltway traffic, nevertheless, is expected to continue to be slowed on the Maryland-bound outer lanes of the Woodrow Wilson Bridge, where repair work recently started.

Drivers headed for Maryland and Delaware beaches are likely to face backups extending from one to three miles tonight and tomorrow morning at the Chesapeake Bay Bridge, officials said.

The Kent Narrows drawbridge will open on a revised schedule aimed at easing traffic backups. Today it will open hourly from 6 a.m. to 3 p.m. and then will remain closed until 8 p.m., when it will open once again, a Coast Guard spokesman said. Tomorrow the bridge will be raised hourly from 6 a.m. to 9 a.m., once at noon and then hourly from 3 p.m. to 8 p.m. On Sunday and Monday it is scheduled to open hourly from 6 a.m. to 1 p.m. and then stay closed until 8 p.m., when the final raising will occur.

The amount of time the bridge is up will vary markedly, officials said. Most of the openings are expected to last 5 to 15 minutes, but officials cautioned that motorists may be delayed by as much as 30 minutes after the 8 p.m. raisings today, Sunday and Monday.

Motorists are likely to face tie-ups on main Eastern Shore roads, especially near narrow bridges at Cambridge and Vienna, officials said.

At Delaware's Rehoboth Beach, city officials have started a new shuttle van service in an attempt to ease traffic and parking problems. Free parking will be provided on Rehoboth Avenue extended near Rte. 1, officials said. Vans taking passengers to the town's center will leave every 15 minutes. Round trips will cost $1.

A Delaware highway spokesman said that the weight limit on the Rte. 1A drawbridge north of Rehoboth has been reduced to three tons. Recreational vehicles exceeding the limit should use an alternate route across a Rte. 1 bridge to reach the beach area, the spokesman said.

On Monday, several major streets in the District will be temporarily blocked off because of parades and other events. Constitution Avenue NW will be closed between Seventh and 17th streets from about 9:30 a.m. until about 2 p.m. because of the Independence Day parade.

Along the parade route, traffic on north-south streets will be halted at Pennsylvania and Independence Avenues. Northbound traffic on the 14th Street bridge will be diverted to the Southwest Freeway and then to the I-395 tunnel under the Mall. The 12th Street exit from the eastbound lanes of the Southwest Freeway will also be closed.

In the Takoma Park area, another July 4 parade will result in temporary closings of portions of Carroll Avenue and Maple Street in the District and suburban Maryland from about 9:30 a.m. to about 11:30 a.m. Monday.

An Independence Day parade will also cause a temporary shutdown of the westbound lanes of MacArthur Boulevard between Whitehaven Parkway and Edmunds Place from about 10:30 a.m. to about 12:30 p.m. Monday.

In the downtown Washington area, pro- and anti-marijuana demonstrations on Monday may lead to brief interruptions of traffic along Pennsylvania Avenue and other streets, officials said. Emergency no-parking signs will be posted near parade routes and Metrobus staging areas, officials added.

"There will be an awful lot of parking that will be restricted in the downtown area," said D.C. traffic engineer Charles Stuart.

The July 4 fireworks display on the Mall is expected to cause widespread traffic tie-ups Monday evening. A National Park Service spokesman said that 17th Street NW will be closed to traffic from about 1 p.m. until Monday evening between Constitution and Independence Avenues to allow placement of fireworks equipment. Traffic may also be periodically barred from 15th Street NW between the two avenues Monday, the spokesman said.

The Metro transit authority has announced plans for special July 4 service with fares set at 50 cents on buses and subway trains. Barrels will be placed in rail stations to collect the fares. Flash passes may also be used.

Metro's rail service will operate Monday on what officials term an augmented Saturday schedule. Red Line trains will run every 10 minutes from 8 a.m. to 6 p.m. and every five minutes from 6 p.m. until late evening. On downtown sections of the Blue and Orange Lines, trains will operate every six minutes from 8 a.m. to 6 p.m. and every four minutes after 6 p.m. Yellow Line trains will run every 12 minutes from 8 a.m. to 6 p.m. and every eight minutes after 6 p.m.

A free shuttle bus will travel between the Pentagon's north parking lot and the Metro subway station at Arlington Cemetery, starting at 8 a.m. Monday. Metro plans to provide additional bus service on major routes during the day, and extra buses will be stationed near downtown subway stops to provide service after the fireworks display.

Montgomery County's Ride-On system plans to operate Monday on an extended Sunday schedule. Service will be provided on six bus routes in the Silver Spring area, connecting with the Silver Spring or Takoma Metrorail stations. The routes are 5, 9, 12, 15, 16 and 17. Officials said inbound service will continue until 8 p.m. and outbound service until midnight.

Virginia officials said the carpool lanes on Shirley Highway (I-395) will be kept open for southbound traffic until early Tuesday to allow Northern Virginia residents to return home after the fireworks display.

For vacationers traveling on I-95 through the state of Connecticut, the American Automobile Association has recommended an alternate route to avoid a Connecticut Turnpike bridge, a section of which collapsed Tuesday. AAA spokesman Tom Crosby suggested that drivers detour onto I-287 and then travel on the Merritt Parkway and U.S. 7 before returning to I-95.