Paccar Inc., citing adverse economic conditions and a decrease in demand, has pushed back to late 2010 the expected opening date of its diesel engine plant near Columbus.

Although the plant originally was scheduled to begin operations late this year, the facility likely will not open until “late in 2010,” says Alan Treasure, spokesman at the company’s Bellevue, Wash., office.

The plant will manufacture 12.9-liter and 9.2-liter diesel engines for Kenworth, Peterbilt and DAF vehicles.

Paccar officials in 2007 signed a contract with the state to provide 500 jobs at the plant by 2013.

Treasure says workers are installing and checking equipment at the nearly complete facility.