An experiment with plastic blocks by an Encino church may give Caltrans the ability to build lighter, cheaper sound walls to tone down the noise of freeway traffic.

Bethel Lutheran Church is building a 13-foot-high wall of polyurethane blocks between the Ventura Freeway and the church and its school, the first use of the lightweight blocks for a sound wall in the United States, according to Caltrans and the block manufacturer.

Caltrans officials--who suggested that the church experiment with the new building blocks for them--said Monday that if the church's wall works and proves sturdy enough, it may be a prototype for faster and cheaper construction of the many expensive sound walls that the state has been asked to build along freeways.

"If it works out fine, then our headquarters will be interested" in other applications, said Bill Minter, who oversees the placement and construction of sound walls for Caltrans in Los Angeles and Ventura counties.

Caltrans allowed the church to build the wall on state property in exchange for using the blocks, which are manufactured in Costa Mesa by a Canadian firm and received their U.S. patent last week. Total cost to the church will be about $65,000--about $85,000 less than if standard concrete blocks had been used, said Kim Schafer, chairman of the church's sound wall committee.

Amin J.A. Shivji, president of Canadian Insulock Corp., which manufactures the plastic blocks, said that using them can reduce the cost of building a wall 20% to 30%. If the blocks eventually become widely used, Minter said, they could free up money to allow more sound walls to be built in neighborhoods where freeway noise is a nuisance.

The yellow blocks, made of a material that resembles plastic foam packing materials, are about the same size as 35-pound concrete blocks, but weigh only 2 ounces. They lock together without mortar, much like children's toy building blocks. But when reinforced with concrete and metal rods, as they will be for the church's sound wall, the blocks are as strong as standard blocks, Shivji said.

Steel reinforcing rods are placed through holes in the blocks and connect with steel rods in a concrete foundation. Concrete is poured into the hollow blocks to add strength. To protect the plastic from damage by the rays of the sun, the wall will be coated with stucco, Shivji said.

So far, the blocks have been used in only one other sound wall--in Ontario, Canada--and a dozen or so experimental houses in Washington and British Columbia.