WASHINGTON (Reuters) - Defense Secretary Donald Rumsfeld may move to extend the investigation of abuses of Iraqi prisoners to include top military ranks, defense officials said on Thursday.

Rumsfeld is considering a request by the commander of U.S. forces in the Middle East to replace a two-star Army general investigating the prisoner abuse scandal.

The move, sought this week by Army Gen. John Abizaid, would replace Maj. Gen. George Fay with a more senior general and open the way for questioning of top U.S. officers to help determine who is responsible for the scandal.

Under Army regulations, Fay, whose report was expected this month, is prohibited from questioning officers above his rank. The defense officials, who asked not to be identified, said the report could be delayed for a month if Rumsfeld gives his approval as expected.

In a major scandal that has sparked outrage in the Arab and Muslin world, U.S. military police have been accused of hooding, stripping naked and sexually humiliating prisoners at Abu Ghraib prison near Baghdad. Several investigations are under way and have extended to other jails in Iraq and Afghanistan.

The requested change in investigation leadership was reported on Thursday by the New York Times and Washington Post.

Fay has been investigating not only the abuse at Abu Ghraib by military police, but to what extent U.S. military intelligence troops might have been involved in either ordering the abuse or taking part. Military police, one of whom has already pleaded guilty and been sentenced to a year in prison, said they were obeying orders.

GROWING U.S. CRITICISM OF SCANDAL

The request by Abizaid comes amid growing criticism from some members of the U.S. Congress and grumbling by military officers that the investigation of Abu Ghraib could end up punishing only a handful of enlisted soldiers and leaving senior officers unaccountable.

Pentagon officials confirmed the New York Times report that three-star Lt. Gen. Ricardo Sanchez, the ground commander in Iraq, had taken the unusual step of asking to be removed as the reviewing authority for Fay's report and requesting that higher-ranking officers be appointed to conduct and review the investigation.

Sanchez, who last year ordered military intelligence to take control of Abu Ghraib, has denied any knowledge of the abuse before the scandal broke early this year.

Sanchez also told Congress in sworn testimony that his order regarding military intelligence was only to assure security at the prison and not to insert military police into the role of conducting interrogations or "softening" prisoners for questioning.

Meanwhile, a class action suit filed in San Diego on Wednesday accused two U.S. defense contractors of conspiring with U.S. officials to torture and abuse Iraqi prisoners.

The suit alleged that San-Diego based Titan Corp. and CACI International of Arlington, Virginia, engaged in "heinous and illegal acts" to show they could get intelligence from detainees, and thereby obtain more government contracts.