WASHINGTON — President Obama is prepared to move ahead with a limited military strike on Syria, administration officials said on Thursday, even with a rejection of such action by Britain’s Parliament, an increasingly restive Congress, and lacking an endorsement from the United Nations Security Council. Although the officials cautioned that Mr. Obama had not made a final decision, all indications suggest that the strike could occur as soon as United Nations inspectors, who are investigating the Aug. 21 attack that killed hundreds of Syrians, leave the country. They are scheduled to depart Damascus, the capital, on Saturday. The White House...