America's 205th Independence Day tomorrow is expected to have more fireworks, more music, more special events and more people to marvel at them than any Washington Fourth of July celebration since the Bicentennial bash of 1976.

The National Park Service, orchestrator of the annual fireworks extravaganza on the Mall, expects close to 500,000 spectators for the show.

The big events this year -- besides a fireworks display billed as "bigger and better" -- are a repeat of last year's concert by the Beach Boys, the nation's longest-running rock-and-roll group, as well as concerts by two other rock and two jazz bands and the National Symphony. There also is a 10 a.m. parade down Constitution Avenue and the Smithsonian Institution's 15th annual American Folklife Festival, which for the last four years has been held in the fall.

In response to many complaints last year, the Park Service is renting close to 400 portable toilets -- almost twice the number leased in 1980, when crowds waited in lines of more than 200 to use the restrooms near the Washington Monument.

The American Red Cross will have six large Army tents, instead of last year's three, to care for the sunburned, lost and injured. Heat prostration and cut feet were the most common ailments at the 1980 Independence Day celebration and the Park Service this year is prohibiting glass bottles on the Washington Monument grounds.

Then there are the fireworks -- "music and color-coordinated, electronically timed" fireworks with longer and more high aerial displays than in previous years, said Donna Grucci of Long Island's famous fireworks family. p

The Gruccis, who ushered in the Reagan administration in January with a $160,000 inaugural fireworks display, won the 1979 world competition of fireworks at Monte Carlo, the first time an American firm has won.

The Gruccis won the Park Service's fireworks contract for the third year in a row in "probably the most heatedly contested award I've ever seen," said Frederick Schwartz Jr., a U.S. Department of Transportation attorney and fireworks buff.

Schwartz, who for years complained to the Park Service about the "dull fireworks" seen on the Mall, heads the technical evaluation committee that advises the federal government on who can offer the best Fourth of July display.

The committee was set up after the Bicentennial fireworks display, put on by a French firm, fizzled for many of the 1 million viewers -- the largest crowd in Washington history -- because it was too low for many to see. Since 1979, the Gruccis have beat out the granddaddy of American fireworkers manufacturers, the Zambelli family of New Castle, Pa., which had put on Washington's Fourth of July show for 16 of the 17 years before 1979.

The Park Service's $20,000 pyrotechnical performance "will have fewer fireworks with reports, ending with a big bang, and more comets, crossettes" and other spectacular aerial shells, said Donna Grucci.

The 500 pounds of fireworks will include 1,790 shells exploded in time with music broadcast over loudspeakers strung between the Lincoln Memorial and Washington Monument. The music will be played simultaneously over WMAL radio for those out of earshot of the loudspeakers. The fireworks will include more 12-inch shells, which shoot twice as high as the Washington Monument, than in past years.

Free subway and bus rides after the fireworks will end this year. Metro has provided them since the subway system opened in 1976. The free rides home, however, cost Metro about $100,000. Bus and subway riders will pay 50 cents throughout the day, with free transfers. The subway farecard machines will be bypassed for the holiday.

The subway will operate until midnight and free parking will be available at the north Pentagon parking lot and the South Capitol Street fringe parking, with Metro shuttle buses connecting to the subway. No free parking will be available at RFK Stadium this year, because the Dips soccer team has a 5 p.m. game.

Downtown parking will be restricted along portions of Eighth through 13th streets, D and E streets and Constitution and Independence avenues. Only two streets will be closed during portions of the day, Constitution Avenue during the parade and 17th Street between Constitution and Independence Avenues during the fireworks.

Private groups also are planning rallies in downtown Washington today and tomorrow. A Vietnam veterans coalition will hold a rally tomorrow from 6 a.m. to midnight on the Constitution Gardens site of the future Vietnam memorial and a pro-ERA rally will be held in Lafayette Park and on the White House sidewalks from 10 a.m. to 5 p.m.

The annual marijuana smoke-in of the Youth International Party (Yippies), will be held from 9 a.m. to midnight today in Franklin Park and near the Reflecting Pool and tomorrow from 6 a.m. to 3 p.m. at Franklin Park followed by a 2 p.m. march down Pennsylvania Avenue to Rawlins at 18th and E streets NW.