Julia Wesaw, 77, of Hartford, Mich., beamed yesterday as she described taking the first airplane flight of her life to celebrate this Fourth of July in Washington, where she has spent six days weaving Potawatomi Indian baskets at the American Folklife Festival on the Mall.

"Oh we're having a great time," Wesaw said as she took a busman's holiday to watch a Laotian American basketmaker demonstrating his craft.

"It looks easy to him, but I probably couldn't do that," she said.

While other visitors wandered sluggishly through the Mall's 91-degree haze, slurping lime-fizzes, munching watermelon and puzzling over Metro maps, the National Park Service continued preparations for tonight's scheduled fireworks display and hoped against a possible rainout.

"We'll be 99 1/2 percent finished by 5 p.m.," William I. Newman, the Park Service's chief of maintenance said yesterday as about 50 of his workers continued installing crowd-control fences, portable toilets and lighting fixtures needed for the 450,000 guests expected for today's events on the Mall.

The National Weather Service predicts hot and humid conditions today, with a 40 percent chance of afternoon or evening thunderstorms.

"Oh yes, it's quite possible" that rain could postpone the fireworks until Sunday night, said forecaster Scott Prosise.

In an attempt to move the crowds expected today, Metro will operate from 8 a.m. until 3 a.m. Sunday, will dispense with Farecards and will charge a flat 75 cents for all subway and bus trips.

Subway fares will be collected in exact change and tossed into barrels. Free transfers between bus and rail will be offered, and will be accepted by Alexandria DASH, Montgomery County Ride-On and Fairfax Connector buses as well as Metrobuses.

If the Park Service's 4,500-shell fireworks show is rescheduled for tomorrow, Metro will continue to charge the uniform 75-cent fare, and will remain open until everyone gets home.

Metro advises riders to linger on the Mall after the fireworks, rather than try to leave the Mall as soon as the fireworks end.

"It takes hours for people to arrive, but they all want to leave in the same 15 minutes after the fireworks," said spokeswoman Beverly Silverberg.

The system can move 100,000 riders per hour, so it will take three hours if 300,000 people try to take Metro home tonight, she said.

Metro officials, who started planning this year's Fourth of July service on July 5 last year, recommend that riders to avoid the busiest stations, such as Smithsonian and Metro Center, and to avoid transferring from one line to another.

For example, they said, a rider bound for Vienna should enter the system at a station where it is possible to board an Orange Line train and seek to avoid transfers within the rail system.

Even if post-fireworks crowds pack the Metro platforms and slow subway service to a crawl, riders can feel lucky compared to some of the area residents who elected to spend the three-day weekend out of town.

Some of those would-be travelers kicked off the nation's 211th birthday party by sleeping most of the night at Dulles International Airport or fuming in backups on the Capital Beltway.

Bad weather in New York Thursday night delayed Continental Airlines Flight 891 for almost six hours, leaving an unknown number of passengers waiting at Dulles until 3:52 a.m. yesterday, the second night in a row that Texas Air Corp. customers were found angrily pacing the Dulles terminal overnight because of weather-related delays.

The Boeing 737 was scheduled to leave La Guardia Airport at 7:20 p.m. Thursday and pick up passengers at Dulles, before leaving at 9:15 p.m. for Tampa, Fla. Thunderstorms delayed its La Guardia departure until 2:22 a.m. yesterday, so it did not reach Dulles until 3:25 a.m., said a spokeswoman for Continental, which is owned by Texas Air.

On Wednesday, Eastern Airlines Flight 28 from Miami to La Guardia was forced by weather to make an unscheduled stop at Dulles, stranding 153 passengers there from 9:06 p.m. until 7:52 a.m. Thursday, said a spokeswoman for Eastern, which is also owned by Texas Air.

The airline did not provide hotel accommodations because no hotel rooms were available nearby and because of uncertainty about the departure time, said Eastern spokeswoman Karen Ceremsak.

Beach-bound drivers were stuck for almost four hours yesterday morning by a five-vehicle accident on the Beltway near Rte. 50.

But even that provided only a slight respite in the traditional logjams at the Severn River bridge and Eastern Shore roads.

Chesapeake Bay Bridge officials estimated that more than 70,000 cars passed through the toll booths on Thursday, and although far fewer drove through yesterday, most beachgoers tried to leave Washington early, and arrived at the bridge together.