WASHINGTON (AP) _ Picture this: An American flag big enough to cover a football field and most of its bleachers. A flag so big you could wrap two space shuttles in it or harvest 250 bushels of corn from under it. So big that its stripes are 16 feet broad and its stars 13 feet bright.

The ''Great American Flag'' was unfurled today on the Washington Monument grounds as an observance of Flag Day. It was laid on the ground because engineers worry the monument might tip over if it were used as a pole for a flag that size.

This is a humongous flag, the biggest in the world, according to the Guinness Book of Records. Members of the Iron Workers Union who've made it a project to lay out the flag every time it's shown were there 100 strong by dawn's early light to pull and tug it into position.

But the supersalesman who thought of the flag, fired up others about it and got it made in 1980, wasn't there to see it.

''I've really been pushed out of this thing,'' said Len Silverfine, who runs a public relations-advertising firm, the Big Idea Co., in northern Vermont. ''I've never received an invitation, although I was called the other morning and told it was in the mail.''

Flag Day commemorates the adoption by the Continental Congress in 1777 of the Stars and Stripes as the United States flag. Silverfine's flag history goes back to the bicentennial in 1976 when he wanted a big, big flag to welcome the tall ships to New York harbor.

''When this flag was conceived in the mid-'70s, the best you can say is that the majority of the population was sort of indifferent to the flag,'' he said. ''It's tough to be indifferent to a flag that's 411 feet long and 211 feet high.''

The 1976 flag was hung from the Verrazano-Narrows Bridge in New York City. What so proudly they hailed at the twilight's last gleaming was torn to shreds by the wind.

Undeterred, Silverfine began anew, raised money and got volunteers at Anchor Industries in Evansville, Ind., to sew up another ''Great American Flag.''

''Big, colossal, gargantuan things have a way of capturing people's imagination the way normal size objects cannot,'' he said, pointing out that a one-eighth-scale model of the Statue of Liberty stands on an island in the Seine River in Paris but that nobody knows it.

He brought the flag to Washington in 1980 for Flag Day and with the help of ironworkers and tourists got it unfolded by the monument. It made a few more appearances after that and then was stored and forgotten by everyone but Silverfine.

He decided to present it to the United States and at a White House ceremony in 1983 President Reagan accepted it. ''I promise you your government will keep it and treasure it and use it as a reminder of the greatness that is America,'' Reagan said.

The flag was stored in a General Services Administration warehouse in Landover, Md. It was hauled once to North Carolina where, Silverfine said, a group ripped it while trying to lift the seven tons of polyester with three cranes.

Silverfine said GSA took the flag back but ''never did they try to repair it, inspect it or do anything to wash it.''

Last June, Silverfine told the flag story to the Evansville Courier, which headlined it ''The Two-Acre Forgotten Flag.'' The Associated Press did a story, too, and Silverfine sent the clippings to Sen. Dan Coats, R-Ind. The senator got in touch with the U.S. Park Service and today's affair was born.

In February, Silverfine told the GSA he'd like to get the flag cleaned and repaired for its showing. The flag was trucked to Humboldt, Tenn., where ''virtually the whole town,'' according to Silverfine, volunteered and scrubbed it clean.

Then came the big problem. Silverfine said the GSA haulers came early and the flag wasn't dry. Protests were ignored and the flag was loaded while still wet. Silverfine was mad, but GSA spokeswoman Katherine Gaddy said the flag was U.S. property now, and the government needed it back.

After a week, when GSA workers opened the truck doors, the mildew smell was overwhelming.

Desperate, the agency called in the Marines, who provided a parade ground at Quantico, Va., to lay out the flag. In two days the flag was gallantly streaming, figuratively.

There is red glare and tempers bursting in air between GSA and Silverfine. That's why he wasn't attending today's ceremony.

''They muscled their way in, they took over control from Senator Coats' office and the Park Service,'' Silverfine said.

''He kept saying we are cutting him out of the event,'' Ms. Gaddy said. ''It's not his event, not ours. It's Senator Coats' event.''