HARTFORD, Conn. (AP) — Two key U.S. senators have called on Defense Secretary Leon Panetta to consider barring a United Technologies Corp. subsidiary from Pentagon contracts for illegally exporting software to China.

Michigan Democrat Carl Levin, chairman of the Senate Armed Services Committee, and Arizona's John McCain, the top Republican on the panel, asked Panetta on Monday to evaluate the case for contract suspension or debarment of jet engine maker Pratt & Whitney Canada.

Levin and McCain called the illegal exports "enormously troubling."

Hartford-based United Technologies would not comment, and a Pentagon spokesman did not respond to a request for comment.

Pratt & Whitney Canada pleaded guilty on June 28 to crimes related to the illegal export of software that U.S. officials say was used by China to develop its first modern military attack helicopter.

"As we (are) sure you do, we find the crime to which PWC pleaded guilty enormously troubling," Levin and McCain wrote to Panetta and Secretary of State Hillary Clinton. "The nature and number of these export control violations and the length of time during which they occurred raise the concern that they may have caused significant harm to our national security."

Pratt & Whitney Canada Corp., UTC and another subsidiary agreed to pay more than $75 million in fines in connection with the export violations and providing misleading information to the U.S. government.

The United States has barred the export of defense articles to China since 1989.

Sen. Richard Blumenthal, D-Conn., and a member of the Armed Services Committee, said Tuesday he agrees with Levin and McCain that any harm that may have occurred due to the exports should be assessed and he backs stronger oversight of export controls.

He also said he agrees that the violations were "enormously troubling" but does not back the two senators' request that the Pentagon consider suspending UTC's work or halting its contracts.

"Debarment and suspension are typically used to protect against ongoing or threatened violations by a company involved, and I am unaware of any specific evidence or indication of ongoing or threatened violations," Blumenthal said.

United Technologies, which posted $58.2 billion in revenue last year, is one of the biggest companies and employers in Connecticut.

The Department of State announced on June 28 it is barring Pratt & Whitney Canada from certain arms regulations licensing. Levin and McCain cited the agency's action in asking Panetta to consider a similar response.

Authorities said the prosecution was one of the largest involving export violations with a major defense contractor in the Justice Department's history.