WASHINGTON (AP) — U.S. military forces stand ready to strike Syria at once if President Barack Obama gives the order, Defense Secretary Chuck Hagel said Tuesday as the United States prepared to declare formally that chemical weapons had been used in the Syrian civil war.U.S. officials said growing intelligence pointed strongly toward Bashar Assad’s government as the culprit — a claim Assad called “preposterous.” There were cautions from the White House the goals of any military action would be measured, not intended to drive Assad from power.“The options we are considering are not about regime change,” said White House spokesman Jay Carney.The U.S., along with allies in Europe, appeared to be laying the groundwork for the most aggressive response since Syria’s civil war began more than two years ago. The White House said Obama had not settled on what action to take in response to the large-scale use of deadly gases, a move Obama said last year would cross a red line.Officials had planned to release an intelligence report Tuesday more formally linking Assad to the attack, but that release appeared to be pushed back until later in the week.