By Diane Bartz

WASHINGTON, Dec 11 (Reuters) - Pennsylvania's two U.S. senators urged regulators on Thursday to approve "as soon as possible" Comcast's plan to merge with Time Warner Cable, saying there were many potential benefits from the proposed tie-up that is opposed by some consumer groups and rival companies.

Senators Bob Casey, a Democrat, and Pat Toomey, a Republican noted that Pennsylvania-based Comcast Corp has pledged to speed up Internet speeds for Time Warner Cable customers. Their letter to Federal Communications Commission Chairman Tom Wheeler also cited the potential for additional jobs and charitable contributions in their state by the larger company.

In February, No. 1 U.S. cable company Comcast said it planned to buy No. 2 Time Warner Cable Inc for $45 billion. Furious critics complained the mega deal would create a giant with too much control over what Americans watch on TV and where they go on the Internet.

"We urge you to approve the merger as soon as possible," the Senators wrote to the FCC, which must determine whether the deal is in the public interest. It is reviewing the mergers alongside the Justice Department, whose approval is also needed after it conducts an antitrust review.

Critics of the Comcast-Time Warner Cable merger on Wednesday announced a coalition to press regulators to block the transaction. The "Stop Mega-Comcast" coalition includes satellite company Dish Network Corp, consumer advocacy group Public Knowledge and TheBlaze, conservative commentator Glenn Beck's media company.

Comcast has stressed that it does not compete against Time Warner Cable in any market. It says the two companies together would offer better services to more consumers.

Comcast is Casey's biggest contributor, giving him and his political action committees $114,175 for the 2009 -2014 election cycle, according to data from the Center for Responsive Politics.

Comcast was the 7th largest contributor to Toomey in the 2009-2014 cycle, giving him, his campaign committee and political action committee $70,6000, according to the Center for Responsive Politics.

(Reporting by Diane Bartz; Editing by David Gregorio)