IN SAUDI ARABIA, JAN. 21 -- Saudi units assigned to the front lines near Kuwait to demonstrate Arab resolve moved to positions behind U.S. forces the first night of the war, angering some American and British soldiers.

Saudi officials acknowledge the pullback but insist it was, in the words of an official military source, "a planned withdrawal."

American military sources said the U.S. command knew about it in advance, but they did not know how far in advance. The U.S. command has refused official comment.

A Saudi official quoted anonymously by the Saudi Press Agency said the withdrawal was planned well in advance of hostilities and designed to protect the Saudi troops from Iraqi artillery and rocket fire during the air phase of the war.

A U.S. Marine officer in the area said the Saudis pulled back just before allied forces, including Saudi pilots, began a bombing campaign against Iraqi positions in Iraq and southern Kuwait, including some within 50 miles of the Saudi-Kuwait border.

"We're essentially the front now," said a British officer in the border area. "I'd have turned my bloody guns on them and sent them back."

Saudi troops also are stationed to the west, in the Hafr al Batin area about 60 miles south of the Kuwait-Iraq border.

Another Saudi official said, also anonymously, that the withdrawal "was according to the plan." He said "civilians had already been evacuated from the area and this was a plan to evacuate the area."