THE SHIFTING ENEMY

The top U.S. commander in Iraq on Thursday outlined an essential evolution in the insurgency besetting American troops as homegrown guerrillas give way to an increasingly sophisticated opposition originating abroad.

An apparent relationship among groups such as Ansar al-Islam and al-Qaida and Jordanian terrorist Abu Musab al-Zarqawi is "beginning to take precedence" as the source of violent attacks against Iraqi police, army and forces determined to work toward democracy, Lt. Gen. Ricardo Sanchez said in a news briefing Thursday.

The capture of Saddam Hussein in December produced intelligence that helped military analysts track Saddam loyalists and led troops into successful raids. Opportunistic attacks by former regime elements, such as roadside bombings and shootings, dropped in the last couple o months as those arrests mounted, Sanchez said. Nonetheless, such attacks persist at a rate of about one a day.

However, high-profile suicide bombings and coordinated attacks increased in pace and scale, particularly in February, indicating a more sophisticated enemy, Sanchez said. Such violence and the discovery of a memo thought by the military to be written by al-Zarqawi that calls for civil war has bolstered suspicions that Iraq is under siege by outside agitators, he said.

"I think the Zarqawi letter is fairly robust in laying out its strategy," Sanchez said about a 17-page memo believed to be written by the man who has been tied to Ansar al-Islam, a Kurdish militant group that the U.S. has linked to al-Qaida.