HARRISBURG — U.S. Sen. Bob Casey today wrote to a Shell executive in hopes of persuading the oil and gas giant to choose a Pennsylvania site to build a huge new chemical plant that could mean thousands of new jobs and millions of tax dollars for the state.

The company has said it will decide early this year where to build the plant from among sites in Pennsylvania, Ohio and West Virginia, and those states’ officials have lobbied Shell or offered incentives for what could be a massive investment that rivals the region’s largest industrial plants.

“Pennsylvania has everything needed to make it a top choice for Shell’s facilities,” Casey wrote in his letter to Shell executive Mark Quartermain.

“We have a proven work force, access to water, communities with a long history of working cooperatively with industry, an extensive rail transportation network and appropriate real estate.

“Pennsylvania also has an exceptional higher education network which will mesh well with Shell’s commitment to innovation.”

A spokeswoman for Pennsylvania’s other U.S. senator, Pat Toomey, said today that Toomey has been in close contact with state economic development officials who are leading the state’s effort to land the plant, and members of his staff have met with Shell officials.

Shell’s plans are driven by the vast natural gas reserves in the Marcellus Shale.

The main product at the proposed Shell plant would be ethylene, which is used to produce chemicals that go into everything from plastics to tires to antifreeze. Workers would break apart the molecules of the raw gas so it can be turned into various products.