Twenty-nine of the nation’s top scientists — including Nobel laureates, veteran makers of nuclear arms and former White House science advisers — wrote to President Obama on Saturday to praise the Iran deal, calling it innovative and stringent.

The letter, from some of the world’s most knowledgeable experts in the fields of nuclear weapons and arms control, arrives as Mr. Obama is lobbying Congress, the American public and the nation’s allies to support the agreement.

The two-page letter may give the White House arguments a boost after the blow Mr. Obama suffered on Thursday when Senator Chuck Schumer of New York, a Democrat and among the most influential Jewish voices in Congress, announced he would oppose the deal, which calls for Iran to curb its nuclear program and allow inspections in return for an end to international oil and financial sanctions.