More than 50 senators Thursday received a closed-door briefing on Iraq's weapons of mass destruction and ties to Al Qaeda from Secretary of State Colin Powell and Defense Secretary Donald H. Rumsfeld, senior defense officials told Fox News.

A large part of the discussion was what evidence should come forward or can come forward without jeopardizing current operations or future military options on the ground, one defense source said.

The defense official would not get into specifics, but said the briefing did.

Senators said later Thursday the Bush administration needs to convince the American people and U.S. allies that war may be needed against Iraq.

Senate Majority Leader Bill Frist said the secretaries weren't notifying Congress of a decision to use military force in Iraq. The administration said that has not been determined.

Sen. Kent Conrad, D-N.D., said Rumsfeld and Powell laid out a stronger case than the administration had before about why force might be needed to stop Saddam. But he said the information would not be strong enough to persuade reluctant allies, like France -- and did not convince him that the United States should act against Iraq without more support.

"It would seem to me to be by far the better part of wisdom to have an aggressive inspections regime buttressed by our intelligence, so that we are providing them cues on where to go," he said.

The top Democrat on the Senate Armed Services Committee, Carl Levin of Michigan, said the United States has just begun to share information with the U.N. inspectors. "And my view is that there is a significant way to go before we share the information," he said.

Rumsfeld told reporters as he left the Capitol "the inspectors are being provided with an enormous amount of information already."

Sen. Lindsey Graham, R-S.C., said he agrees with President Bush's handling of Iraq, but believes the president needs to explain to the American people "why we as Americans should shoulder the burden -- the money burden, the human sacrifice."

Sen. Patty Murray, D-Wash., said she was concerned about opposition from U.S. allies. "I think it would be very difficult for us to pursue this without military and monetary support," she said.

The chairman of the Foreign Relations Committee, Sen. Richard Lugar, R-Ind., said Powell will continue working with France and other countries on the U.N. Security Council after Monday's report by chief weapons inspector Hans Blix.

The Associated Press contributed to this report.

Bret Baier currently serves as anchor of Fox News Channel's "Special Report with Bret Baier" (weeknights 6-7PM/ET), the top-rated cable news program in its timeslot. Based in Washington, D.C., he joined the network in 1998 as the first reporter in the Atlanta bureau. Click here for more information on Bret Baier