Democratic Sen. Patrick Leahy, the most senior member of the Senate, said Sunday the resolution authorizing the use of force in Syria that the administration sent to Congress Saturday will be changed in the Senate in part because it is too open ended.
"I know it will be amended in the Senate," Leahy told reporters after a classified briefing in the Capitol.
Leahy, chairman of the Senate Judiciary Committee, said he is concerned that the resolution isn't limited enough. "I'm concerned at this point it's too open ended," he said.
Rep. Chris Van Hollen, D-Md., a member of the Democratic leadership who has typically supported President Barack Obama, also said the resolution needs to be rewritten to possibly include an expiration date and an express prohibition on using ground troops.
The authorization needs, "at the very least, clear language that the American troops will not be on the ground," he said, calling the current language "a partial blank check" for the administration. "It needs to be more narrowly drawn."
The comments from Leahy and Van Hollen were among the strongest examples of the broad skepticism that many members of Congress expressed after emerging from an hours-long classified briefing held in the bowels of the Capitol on the Sunday of Labor Day weekend.
Eighty three members of Congress attended the classified briefing, according to House aides.
The briefing came just hours after the White House sent Congress a two-page resolution Saturday night that would authorize the use of force in Syria to "prevent or deter the use or proliferation" of weapons of mass destruction -- "including the transfer to terrorist groups or other state or non state actors."
Obama's abrupt reversal on Syria -- American ships had already staged in the Middle East before he decided to ask Congress to weigh in on strikes -- sets up votes for after Congress returns on Sept. 9.
A Leahy spokesman said that the administration "understands" that there will be new language drafted in the Senate, and a senior administration official told NBC News that didn't come as a surprise.
Some expressed support for the president, including Reps. Debbie Wasserman Schultz of Florida and Eliot Engel of New York.
"To me, the searing image is as a mom of babies lined up dead," Wasserman Schultz said.
But many in both parties were skeptical - and looking for clear limits on the intervention.
"I'm looking for a resolution that makes it clear that this is not a declaration of war," said Rep. Xavier Becerra, D-Calif., a member of the House Democratic leadership.
"I have just attended a classified congressional briefing on Syria that quite frankly raised more questions than it answered," Sen. Tom Harkin, D-Iowa, said in a statement.
There was uncertainty on the GOP side as well.
"I'm a no," said Rep. Michael Burgess, R-Texas.
Many of the members who attended the briefing flew back to Washington specifically to view classified documents and question administration officials, including Deputy National Security Adviser Tony Blinken. Some, including California Rep. Kevin McCarthy, took red-eye flights from the West Coast to attend.
The briefing allowed members -- who have been at home during a month-long August break -- to review classified material that couldn't be securely transmitted over the phone.
More briefings and meetings are planned for the coming days as the administration looks to make its case to Congress. Earlier on Sunday, Secretary of State John Kerry said samples collected by first responders after the reported Aug. 21 chemical weapons attack in Syria have tested positive for the nerve agent sarin.
Senate Majority Leader Harry Reid said in a statement Saturday that the Senate would hold hearings in the Senate Foreign Relations Committee beginning Tuesday. Oklahoma Republican Sen. James Inhofe said the Senate Armed Services Committee planned meetings for Wednesday; he's the panel's ranking member.
Sen. John McCain, R-Ariz., said Sunday that he and Sen. Lindsey Graham, R-S.C., had been invited to the White House to discuss Syria. The two have been longtime critics of the administration's actions in Syria, criticizing the president for not doing enough to intervene in a conflict that's now killed more than 100,000 people. The two senators put out a joint statement Saturday saying that limited strikes wouldn't go far enough.
But McCain was measured during a Sunday appearance on CBS' "Face the Nation," indicating that the consequences of opposing the president might be greater than taking limited action.
"The consequences of Congress of the United States overriding a decision of the president of the United States of this magnitude are really very, very serious," McCain said.
Meanwhile, Sen. Rand Paul, R-Ky., a critic of the Obama administration's push for action on Syria, said on Sunday morning that he expected the Senate to approve the resolution but predicted there would be more dissent in the House.
"I think it's at least 50/50 whether the House will vote down involvement in the Syrian war," Paul said on NBC's Meet the Press.
"I think the Senate will rubber stamp what [Obama] wants but I think the House will be a much closer vote," he added. "And there are a lot of questions we have to ask."