As the administration of President Barack Obama launched what it described as a "flood the zone" campaign to persuade Congress to authorize military action against Syria, officials said Monday that they are willing to rewrite the proposed resolution to clarify that any operation would be limited in scope and duration and would not include the use of ground troops.

Their signal of flexibility came amid indications that Obama is picking up tentative, conditional support in what promises to be a difficult battle for approval of military strikes.

After meeting with the president Monday at the White House, Republican Sen. John McCain — who has been among the leading Syria hawks — warned that if Congress rejects the resolution, "the consequences would be catastrophic. The credibility of this country with friends and adversaries alike would be shredded, and there would be not only implications for this president but for future presidencies as well."