Jan 27 (Reuters) -

The U.S. energy regulator has reinstated the certificate for

Williams Companies' ( WMB ) Transcontinental Gas Pipe Line

(Transco) on Friday, the company said on Monday, which would

allow the expansion of the project.

Last year, a U.S. appeals court said the Federal Energy

Regulatory Commission (FERC) should have better assessed the

risk of significant greenhouse gas emissions, throwing out its

"arbitrary and capricious" approval of the Regional Energy

Access (REA) expansion project.

The company had sought a temporary emergency certificate

with the FERC to continue operating its project, in September.

Williams designed REA to help meet rising gas demand and

ease supply constraints affecting customers in Pennsylvania, New

Jersey and Maryland.

The company said the project, one of the biggest under

construction in the U.S. Northeast, will provide enough gas to

serve 4.4 million homes annually.

The company said on Monday, the order, for the $1 billion

natural gas project, will take effect immediately upon the

issuance of the mandate by the D.C. Circuit Court of Appeals.