A five-day exposition on the building arts will open Wednesday at the Pension Building, 4th and F streets NW.

It is sponsored by the Committee for a National Museum of the Building Arts and the Washington Building and Construction Trades Council. Visitors will be able to participate in demonstrations and discussions with Bricklayers, ironworkers, painters, sheet-metal workers, carpenters and steamfitters.

Demonstrations include the assembling of a steel cage, soldering of pipes and the making of neon signs.

Cynthia R. Field, president of the museum committee, which is seeking to have Congress designate the Pension Buildings as a national museum for the building arts, said that the fair will be open from 10 a.m. to 4 p.m. through July 8. She said the fair will also offer visitors an opportunity to see the Pension building's unusual architectural styling - and "how much it needs preservation work."

Field said that the rroof has been leaking, causing water damage to the century-old brick structure.It was designed by U.S. Army engineer Montgomery Meigs to serve the nation's war veterans and their dependents after the Civil War.

Veterans Administration is no longer located there and the Pension Building is occupied by other government offices as well as the museum committee.

Seven inaugural balls have been held in the building's expansive interior court, which is the site of the building trade fair.

Last year Congress endorsed the idea of using the building for a housing and architectural museum but has taken no initiative to fund the project. It is estimated that it will take $3 million a year to operate the museum and $21 million to renovate the building.