With red, white and blue flags waving in great abundance, this normally sleepy Western Maryland community came alive today in an old-fashioned celebration of patriotism widely known as Memorial Day but still recognized here about as Decoration Day, when graves of war dead are ritually festooned with flowers.

It was the 118th annual such commemoration here, marked by a parade up the main street of a town that was caught in the middle of the bloodiest single-day battle of the Civil War. They marched 80 units strong from the public square to the military cemetery where 4,768 Union dead are buried.

Civil War veterans of what the winning North called the Battle of Antietam and the South calls Sharpsburg, are long gone and only Lester Mose, Sr., 89, remains among the town's World War I veterans, but the spirit of the day lives on.

For years, the annual parade drew as many as 10,000 people to this town of 800. Today, under brilliant blue skies, there were 4,000 to 5,000 on hand "to be generous," according to Mayor Gerard Quinn.

"I don't think patriotism ever left this area," said Mary Jane Albert, 59, of nearby Boonsboro, as she waited to watch her granddaughter, a majorette representing the Boonsboro Middle School, pass in review.

Wilbur M. Mumma, whose great-grandfather's farm was burned by Confederates the night before the battle, agreed. "If you think patriotism is dead, just come to Sharpsburg. You'll see flags here in every direction."

Decoration Day in Sharpsburg has been described by Mumma, a local historian of the event, as Christmas Day, Fourth of July, a Sunday school picnic and a family reunion all rolled into one.

"Years back," Mumma recalled, "the night before the parade there were more fights and more drunks. It was just a time for celebrating."

Celebration is a little less boisterous and more family oriented now, perhaps. Mumma's brother, for instance, had returned from Norman, Okla., for the event.

The Hagerstown Exchange Club passed out 750 small American flags to children along the parade route. Other service organizations set up food tables along Main Street and vendors hawked balloons and banners.

"I'd like to have a dollar for every flag in this town," said Gloria Mumma, Wilbur's wife. "I'd be rich. Could retire."

The parade is "probably the biggest thing that happens in this town every year," said Willis Baker, owner of Pete's Tavern, whose sign features figures of Union and Confederate soldiers.

It was here, in September 1862, that 23,000 soldiers were killed or wounded in the battle, after the creek that runs by here and into the Potomac. Five years later, the first parade was held. In 1888, the citizens planted trees along the road from Antietam Station to shade the Civil War veterans, Blue and Gray, who arrived by train to attend the commemoration.

Today, the old train station is converted to apartment units, but many of the trees are still standing, and some 350 Civil War reenactors participated in the commemoration. All wore Union colors.

"There's one Confederate. They made him wear civilian clothes," said Linda Johnson, who had come from Michigan with her husband for the event. While he marched with the "reactivated" Michigan 17th, the volunteer unit that fought here, she sat in period dress on the porch of the Victorian Inn at Antietam, a bed-and-breakfast place whose lawn was filled with costumed wives and girlfriends of the would-be weekend warriors.

As in every parade save two, the Rohrersville Marching Band was on hand. Its uniformed members played "The Battle Hymn of the Republic" and other Union songs, but no "Dixie."

Charles B. Sumner, 73, a self-described "dirt farmer" who plays a big brass horn in the band, said he's missed only two parades since 1929.

"I like it all right, but I can't stand the parades anymore," said Sumner. "Too old."

Francis Saunders, a past commander of the sponsoring American Legion Post 236 and parade organizer from 1947 to 1972, said he missed the horses that once led the line of march. "Everything is motorized now."

If some things change, basic traditions die hard here. For days preceding the big event, residents manicure lawns, paint porches and sweep steps. The white frame and stone houses lining Main Street are much as they were during the battle.

In fact, miniballs can still be found wedged in the second-story window frames and doors of a home belonging to John G. Ray, who operates a Civil War museum and gift shop on weekends and commutes 60 miles weekdays to his job as a microbiologist at the National Institutes of Health in Bethesda.

In keeping with its history, Sharpsburg has a Battlefield Restaurant, a Battleview Market (meats and groceries) and even a subdivision called Confederate Hills, whose main drag is General Robert E. Lee Drive.

Nearby lives Lester Mose, one of 60 from Sharpsburg who fought in World War I and the town's oldest living veteran.

The Sharpsburg Memorial Day program this year was dedicated "with much pride," to Mose, "for his service to his country . . . "