Washington ? The commander of U.S. forces in the Middle East said Wednesday he may need more than the 135,000 troops already in Iraq once political control is handed back to the Iraqis on June 30 because the insurgency is likely to grow even more violent then.

Summoned to testify before Congress on prisoner abuse, Gen. John Abizaid also addressed broader issues, making clear that he believes time is running short to make a viable handover of sovereignty to the Iraqis on June 30.

Abizaid conceded in his testimony that he may have underestimated the strength of the Iraqi insurgency and said U.S. forces were hampered by shortages of military police and other support troops.

As chief of the Central Command running the war, Abizaid said he took responsibility for the abuses at Abu Ghraib prison. Overcrowding in the cells of that jail “contributed to systemic failures,” and may have created conditions for abuse to take place, he said.

Appearing with Abizaid, Lt. Gen. Ricardo Sanchez told the Senate Armed Services Committee that military personnel who received reprimands or similar sanctions for their roles in the abuse may face criminal charges, too.

The troops who detained and interrogated prisoners at Abu Ghraib and their entire chain of command are being investigated, said Sanchez, the most senior U.S. commander based in Iraq. “And that includes me,” he said.

At the same hearing, Sen. John Warner, R-Va., committee chairman, disclosed that the Pentagon had found another disk containing photos of abuse at Abu Ghraib.

The Pentagon told Warner that its criminal investigators in Baghdad were given the new disk “under circumstances that warranted investigation.” Twenty-four photos that apparently show abusive acts by U.S. forces are on the diskette.

Assistant Defense Secretary Powell A. Moore told Warner in a letter to Warner that 13 photos appear to have been already shown on international television. He cautioned that the other 11 “may not be original or true photographs.”

Maj. Gen. Geoffrey Miller, deputy commander for detainee operations for the Multinational Force-Iraq, left, Lt. Gen. Ricardo Sanchez, commander of the Multinational Force-Iraq, center, and Gen. John Abizaid, commander of U.S. Central Command, pause during a Senate Armed Services Committee hearing on Iraqi prisoner abuse. The generals testified Wednesday on Capitol Hill.

A Senate GOP aide said senators would wait until investigators knew the circumstances of the photos before they asked to see them.

At the hearing, Abizaid spoke in somber tones as he assessed the situation in Iraq, offering a sometimes grim view of the challenge in bringing stability to Iraq.

He predicted “the situation will become more violent” after the June 30 handover to an interim government “because it will remain unclear what’s going to happen” between then and the end of the year, when elections are to be held to begin the process of writing an Iraqi constitution.

“It could very well be more violent than we are seeing today, so it’s possible that we might need more forces,” he said, adding that he hoped more countries would contribute troops.

Abizaid said it might take until April 2005 before U.S.-trained Iraqi security forces were fully functioning.

Now, 155,000 coalition troops are in Iraq, and 135,000 of them are American. The Bush administration has had little luck so far in persuading other countries to offer troops.