Perhaps the first major exhibition of paintings by European masters -- certainly one of the earliest -- in North America occurred right here in our front yard, in Prince George's County 170 years ago. The county isn't currently famous, let's all admit, for such cultural exploits.

Metro Scene alluded to the early exhibition in quoting last week from the journals of Mary Bagot, wife of the British envoy to Washington from 1816 to 1819. She went, this column said, with "Mrs. Peter" of Georgetown on April 16, 1816, "to see a collection of pictures" -- some by Van Dyck and Rubens -- at the Calvert Mansion in what is now the town of Riverdale. The estate was then called, with an intermediate "s," Riversdale.

Susan G. Pearl of the Prince George's Historical Preservation Commission adds this detail, referring to Metro Scene's quoting of the Bagot journal:

"It documents the showing of one of the first major collections of Old World paintings in America, the Peeters/Stier collection from Antwerp, which was brought to the U.S. for safekeeping during the French Revolution by H.J. Stier.

"This collection included more than 60 paintings, principally Rubens and Van Dycks . . . . Stier's daughter, Rosalie . . . had married George Calvert of Prince George's County" and lived at Riversdale.

"The collection of paintings had been for the most part kept from the public eye . . . but in 1816, when it was considered safe to ship the collection back to . . . Antwerp, Rosalie was convinced to open her house for two weeks so that the public might view . . . the priceless collection . . . .

"The masterpieces have since . . . found their way into museums all over the world. Contemporary sources suggest that the highlight of the 1816 showing was Rubens' remarkable 'Roman Charity,' now at the Rijksmuseum in Amsterdam."

The Mrs. Peter with whom Mary Bagot visited the art display was Martha Custis (Mrs. George) Peter, who lived at the still-existing Tudor Place mansion in Georgetown. She was a niece of George Calvert and a step-granddaughter of George Washington.

Riversdale, soon to undergo restoration, is at 4811 Riverdale Rd., Riverdale. It's owned by the Maryland- National Capital Park and Planning Commission and is open for tours from noon to 4 p.m. Sundays and by appointment at 779-2011. A Rough Spell

A reader, Edwin Dallas Kennedy of College Park, and a Post colleague, Richard Pearson, both took gentle issue with my referring to Bagot's reprinted journals as containing misspellings. They were, both averred, contemporary phonetic forms of written vernacular.

"Let us not be too critical of the spelling in the English language by those . . . around 1800," wrote Kennedy, noting that Noah Webster didn't publish the first American dictionary until 1828. "In the U.S.," he concluded, "spelling never really became codified until about the middle of the 19th century."

And anybody who has read transcripts of letters sent home or journals kept by those who went for the California Gold Rush or served in the Civil War would have to agree.