SHOW HOUSE HOURS -- The house has been renamed Strathmore Hall, after the cross street, and it will be open as the Decorators' Show House today through Nov. 1. Hours are Monday, Tuesday, Thursday and Friday from 10 a.m. to 3 p.m.; Wednesday from 10 a.m. to 3 p.m. and 6 p.m. to 8 p.m.; Saturday, 10 a.m. to 4 p.m., and Sunday noon until 5 p.m. Admission is $6, with profits going to the National Symphony. No children under 8 years, please.

ABOUT THE turn of the century, the two Corby brothers, William and Charles, made a great deal of money of their industrial patents for bread-baking. As all right-thinking millionaires do, they spent quite a hunk of their money on houses.

William bought and remodeled a magnificent Tudor-style mansion on Chevy Chase Circle, which he named Ishpiming. Charles bought a large estate and a marvelous Classical Revival house on Rockville Pike. The brothers installed hughe his-and-his pipe organs in their Great Halls. Some years ago, the National Symphony Orchestra Women's Committee used Ishpiming as the annual Decorators' Show House.

This year's Decorators' Show House is the other Corby mansion, the one out on Rockville Pike.

Strathmore Hall was built in 1902 as the country home of Capt. and Mrs. James Oyster on 99 acres. The architect was Appleton B. Clark, according to Roy Gauzza Jr., who's doing the landscape design for the show house as well as writing a book, "The Atmosphere of the Gilded Age Estates," forthcoming from Hastings House.

Gauzza said the original frame house is retained in the stair hall, library, back parlor and the back upstairs bedrooms. The south-facing facade with its original wood pillars still faces Washington.

Charles and Hattie Corby bought the house in 1908 to use as a weekend place. In 1914, with the help of Charles B. Keen of Philadelpia, they remodeled the house, greatly enlarging and wrapping a brick envelope around it. Their additions are mostly on the north side of the house. Once the property included 400 acres and 21 buildings, among them a tenant house, pump houses, barns, a golf course and what Marilyn But of the women's committee says was the largest private greenhouse in the area.

After Mrs. Charles Corby's death the houses was acquired in 1943 by the Sisters of the Holy Cross. In conforming to their order's rules, they frosted the glass in the house, including mirrors and glass doors. A later owner, the American Speech and Hearing Association, used it as offices, with the attendant changes. Along the way, the organ was sold, though the fake decorative pipes (standard for organs of that period) remained. t

Ishpiming also went through some hard days. But it kept its organ and, best of all, it acquired sympathetic private owners, Muriel and Dr. John E. Threlfall, who have restored the house in the style to which it had been accustomed under the Corbys.

Now comes the other Corby mansion's good luck. Montgomery County bought the house and 15 acres in 1979 and plans to use it as an arts center. In the meantime, the symphony's women's committee has put the house in fine fettle (or perhaps fine fiddle) with the help of 26 decorators.