WASHINGTON — The Senate voted to block the sale of billions of dollars of munitions to Saudi Arabia and the United Arab Emirates on Thursday, in a sharp and bipartisan rebuke of the Trump administration’s attempt to circumvent Congress to allow the exports by declaring an emergency over Iran.

In three back-to-back votes, Republicans joined Democrats to register their growing anger with the administration’s use of emergency power to cut lawmakers out of national security decisions, as well as the White House’s unflagging support for the Saudis despite congressional pressure to punish Crown Prince Mohammed bin Salman after the killing in October of the journalist Jamal Khashoggi.

A United Nations report released Wednesday made the most authoritative case to date that responsibility for the killing and its cover-up lies at the highest levels of the Saudi royal court.

No other foreign policy issue has created as large a rift between President Trump and Congress, and the vote to block the arms sales deepens the divide. It is the second time in just a few months that members of Mr. Trump’s party have publicly opposed his foreign policy, with both the House and Senate approving bipartisan legislation this spring to cut off military assistance to Saudi Arabia’s war in Yemen using the 1973 War Powers Act, only to see it vetoed.

While the Democrat-controlled House is also expected to block the sales, Mr. Trump has pledged to veto the legislation, and it is unlikely that either chamber could muster enough support to override the president’s veto. Seven Republicans — not nearly enough to override a veto — broke from their party to disapprove of the sales to Saudi Arabia: Senator Susan Collins of Maine, Senator Lindsey Graham of South Carolina, Senator Mike Lee of Utah, Senator Jerry Moran of Kansas, Senator Lisa Murkowski of Alaska, Senator Rand Paul of Kentucky and Senator Todd Young of Indiana.

“This vote is a vote for the powers of this institution to be able to continue to have a say on one of the most critical elements of U.S. foreign policy and national security,” said Senator Robert Menendez of New Jersey, the top Democrat on the Foreign Relations Committee and lead sponsor of the resolutions of disapproval. “To not let that be undermined by some false emergency and to preserve that institutional right, regardless of who sits in the White House.”

The White House announced the sales late last month, and invoked an emergency provision in the Arms Export Control Act to allow American companies to sell $8.1 billion worth of munitions in 22 pending transfers to the three Arab nations. Saudi Arabia and the United Arab Emirates are waging an air war in Yemen that has come under sharp criticism from Congress and human rights organizations.

Members of Congress from both parties have been holding up arms sales from American companies to Persian Gulf nations and trying to end American military support for the Saudi-led coalition that is fighting Houthi rebels in Yemen, which has resulted in what the United Nations calls the world’s worst man-made humanitarian disaster.

By declaring an emergency over Iran, the administration was able to override those holds.

“If we let this emergency declaration go without protest, without a vote, I don’t know that we’re ever getting the power to oversee arms sales back as a body,” said Senator Christopher S. Murphy, Democrat of Connecticut, and one of the authors of the resolution.

Secretary of State Mike Pompeo had pushed hard for the emergency designation, over the objections of career Foreign Service officers and legislators, arguing that the sales would support allies like Saudi Arabia to counter Iran and its partner Arab militias — though some of the munitions would take years to produce and deliver. In the weeks after the declaration was announced, lawmakers have scrutinized the role that a former Raytheon lobbyist played in the decision.

Some Senate Republicans endorsed the administration’s position on Thursday, arguing that rejecting the arms sales would be overly blunt with unintended consequences as tensions with Iran escalate.

The question the Senate will consider, Senator Mitch McConnell of Kentucky, the majority leader, said, “is whether we’ll lash out at an imperfect partner and undercut our own efforts to build cooperation, check Iran and achieve other important goals, or whether we’ll keep our imperfect partners close and use our influence.”

But the administration’s argument ultimately fell flat even for some of the president’s closest allies, like Mr. Graham, who co-sponsored the legislation with Mr. Menendez.

“The reason I’m voting with Senator Paul and others today is to send a signal to Saudi Arabia that if you act the way you’re acting, there is no space for a strategic relationship,” he said. “There is no amount of oil you can produce that will get me and others to give you a pass on chopping somebody up in a consulate.”

The original legislation Mr. Menendez and Mr. Graham introduced would have forced senators to vote on 22 separate resolutions of disapproval, one vote for each arms sale. But a deal struck with Mr. McConnell grouped the resolutions into three votes — and also ensured that the Foreign Relations Committee will take up a bill sponsored by Mr. Menendez that would curtail the ability of the president to use emergency authority to sell arms.

The vote came the same day that Britain announced it would temporarily suspend approval of any new licenses to sell arms to Saudi Arabia, after an unexpected court ruling that ministers had acted unlawfully in allowing the sale of weapons when there was a clear possibility they might be used in violation of international humanitarian law in Yemen.