The revelation came in a letter sent by the top US general in Iraq to other army officials in December 2003, a copy of which was obtained by the Post.

"I cannot continue to support sustained combat operations with rates this low," wrote Army Lieutenant General Ricardo Sanchez, the senior US commander on the ground in Iraq from mid-2003 to mid-2004.

Army units under his command were "struggling just to maintain... relatively low readiness rates" on key combat systems such as M-1 Abrams tanks, Bradley Fighting Vehicles, anti-mortar radars and Black Hawk helicopters, the Post said.

Units were waiting an average of 40 days for critical spare parts, it said. Shelves of some army supply depots were only 60 percent stocked with spare parts.

Sanchez also complained that shipment of protective inserts for 36,000 sets of body armor had been postponed twice in a month.

"I cannot sustain readiness without Army-level intervention," said Sanchez, who has since returned to his permanent base in Germany.

The letter was sent December 4 to the number two officer in the Army and copied to other senior officials, the Post said.

The senior Army logistics officer at the Pentagon told the Post the US army was already aware of the problem and working to correct it when Sanchez's letter arrived.

Supply problems peaked in late 2003 but had largely been addressed since then, Lieutenant General Claude Christianson said.

Part of the cause, he said, was the unexpected intensity of the insurgency, leading to a sharp uptick in the pace of Army operations.

The waiting period for critical spare parts in Iraq is now about 24 days, according to Christianson. All troops in Iraq were equipped with updated body army within seven weeks of Sanchez's letter, he said.

Earlier this month 18 US soldiers refused orders to go on a fuel delivery mission through rebel heartland around the Iraqi capital because of maintenance and safety concerns.

Relatives of the soldiers said they had been arrested for refusing to appear for the mission, a charge denied by army officials who said the "temporary breakdown in discipline" was isolated but had led to a thorough inspection of vehicle safety.

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