A U.S. tour of art objects from museums of the Soviet Union begins this Friday at the Renwick Gallery. More than 20 decorative pieces from the 19th century are in the collection, representing an era in which style often took a back seat to extravagance.

A pair of boxes or "caskets" are from the Hermitage museum in Leningrad and were used to hold small objects such as playing cards. They are delicately carved from bone or walrus tusk, a craft that flourished in the 18th and 19th centuries in northern Russia and was practiced commercially both in Moscow and St. Petersburg.

Another "casket" was made of malachite and gilt bronze at the Peterhof Lapidary Works sometime in the 1840s. There also are vases, candlesticks and clocks from the Peterhof works, most of malachite and bronze, but also one vase in jasper.

Russian niello was practiced as early as the 10th century. Niello, a black alloy of silver, copper, lead, sulphur and occasionally pewter, was applied to engraved gold and silver pieces.When fired, it bonded to the metal beneath it to become the dark backdrop for engravings. A saber, goblet, tumbler and plate - all from the Hermitage - display the niello craft.

The single piece of glass in the collection is a vase from the 1830s made in the Imperial Glass Works in St Petersburg. Much of the Imperial Works' production was for use in the royal court. This vase is made of ruby and green crystal with gilt bronze.

The exhibit, largely of 19th-century paintings and graphics, was organized by the University of Minnesota Gallery and the Soviet Union's Ministry of Culture. It will remain at the Renwick Gallery through Nov. 12. Lectures, Tours and Things

Fear not, ye faithful who have signed up to tour this year's Decorators' Show House at Oxon Hill Manor. The Women's Committee of the National Symphony is handling the event. The Maryland National Capital Park & Planning Commission is providing the house, not accepting tour reservations, as last week's column implied. For more information on visitation, Sept. 24 through Oct. 22, call 387-2932.

The Renwick Gallery shows two films Tuesday in conjunction with its "Buildings Reborn" exhibit. In "Neighbors; Conservation in a Changing Community," residents of Boston's South End are interviewed about what they experienced as their neighborhood changed. "A Place in Time" shows historic preservation as it has been practiced in New Orleans, San Francisco, Williamsburg and Taos, N.M. Both films are free, 11 a.m. and 12:15.

Barbara Nickerson of Expeditions Unlimited in Rockville leads a tour Aug. 15 of some of Washington's old homes that have become museums. The Octagon, Decatur House, the Monroe House and the Anderson House all are on the itinerary. Cost $25, 340-2076.

Folks in Fairfax County celebrate the first anniversary of the opening of Dranesville Tavern today. The tavern, located on Route 7 about 10 miles west of Tyson's Corner, was built in 1824. Restoration by the Fairfax County Park Authority was completed in 1978. Festivities begin at 1 p.m., costs $2, kids $1.50 (430-3576). Next Saturday at 2, the tavern presents an original, humorous play based on 19th-century life there. Same prices. Now Showing

The Committee for a National Museum of the Building Arts displays an architectural history of Canada at the Pension Building through Sept. 15. The exhibit includes color photographs, models and a slide presentation that chart architectural development north of the border - from igloos and teepees to urban sprawl (783-0690).

Tapestries by Venezuelan artist Luis Montiel remain on display on the ground floor of the Inter-American Development Bank, 801 17th St. NW, through Friday.

The Salve Regina Gallery at Catholic University shows recent works by local ceramicist Jeffrey Andrews. Andrews' porcelain and stoneware pieces remain on display through Friday (635-5282). Crafts and Such

A quilt show sponsored by the National Quilting Association continues this week through Friday at the Greenbelt Junior High school in Greenbelt, Md. Patchwork, applique and trapunto are among the techniques represented in 300 quilts. Hours are 10-6 today through Thursday, 10-4 on Friday. The school is at Greenbelt and Edmonston roads, off the Beltway at exit 28, south.

Nan Mahone of Staunton, Va., shows some of her batiks at the Hermitage craft shop in Petersburg, W. Va., today. Among the items for sale are framed batik pieces, screen panels, pillows, clothing and aprons. Hours are 10-5 (304-257-1711).

Silversmith Tom Furlow and potter Michael Olson are among the craftsmen showing their work next Sunday at the Hugs and Kisses shop in Upper Marlboro. Hours are noon till 8 p.m. Call 301-261-6109 for more info. Those Old Collectibles

An exhibition and sale of Oriental art is scheduled for this Friday through Aug. 11 at Woodward & Lothrop's Montgomery Mall store in Bethesda. About 500 pieces are in the collection, including both antique and modern works from Japan, China, India, Tibet, Nepal and Thailand. The oldest prints include Chinese woodcuts and Indian miniatures dating to the 18th and 19th centuries. Open during regular store hours. CAPTION: Picture, This Ruby and green cystal glass vase with gilt bronze, made in the 1830s, is part of "The Art of Russia" exhibit at the Renwick Gallery. It was lent by the Hermitage museum in Leningrad.