The tribute was to have been an elegant lawn party in the style that was customary for the southern gentry who summered at the fashionable Ontario apartment building around the turn of the century.

But Saturday's downpour forced organizers of the 80th-birthday celebration of the grand old building at 2853 Ontario Rd. NW in Adams-Morgan to move the affair inside.

More than 100 residents gathered in the once-posh public dining room, where former residents Gen. Douglas MacArthur, Admiral Chester W. Nimitz and the widow of Gen. George E. Pickett, leader of the famed Gettysburg charge, presumably dined. Today it is an unpretentious activities room where the building's cooperative membership meets regularly to hammer out budgets and settle minor disputes.

The purpose of Saturday's festivities, however, was simply to usher in the ninth decade of one of the city's grand old architectural creations and to revel in its colorful past.

The champagne reception coincided with the publication of the first documented history of the Ontario, a seven-year effort by the building's history committee, headed by a young educational-testing professional, Penelope Engel.

"Like a lot of people here, I just love this place," said five-year-resident Engel. "I'd come home at night, look up at it and start wondering who designed it, who built it, and who lived where. And one question just led to others."

The research substantiated the long list of legendary judges, congressmen, journalists and military heroes who lived in the six-story brick and stucco high-rise.

It also cleared up a few mistaken notions: The Pearl Buck who once lived here was no relation to the late noted author nor is there any indication that a famous general's horse is buried beneath the rear parking lot.

It remains the home of Watergate journalist Carl Bernstein, however.

"It was a high-class place," said 60-year resident Robert Aten, recalling the 1920s when the most prominent resident was Adm. Joel T. Boone, White House physician to Presidents Harding, Coolidge and Hoover.

Today, the Ontario is one of the best preserved among the large luxury apartments of its era in the city, according to John Goode, a Smithsonian curator and architectural historian. But its conversion into a cooperative 30 years ago has fostered an atmosphere more like that of a small town, said Clarence Streit, who has lived there 41 years with his wife, Jeanne.

Although it has never been able to isolate itself completely from the rise and fall of the area around it, the building's luxurious appearance still stands in contrast to much of its surroundings.

The ethnic mix of the Adams-Morgan neighborhood attracted many of the young professionals who moved to the Ontario in the '70s, Engel wrote. But many of the older residents remained because of the vestiges of the building's tonier past, she added.

"Oh, it's lovely, really lovely," gushed one woman as she walked through the former quarters of MacArthur and his mother on a tour during Saturday's festivities.

The only ghost that Engel said she unearthed was the Ontario's continuing image as a bastion of elegance. "You still feel it now and then," she said, "but not nearly as much any more."