The delay is a sign that Democrats are struggling to win Republican support for the agreement.
Sen. John Kerry, Massachusetts Democrat, who chairs the Foreign Relations Committee, now plans a vote for the “New START” treaty after lawmakers return in September from a recess. The vote was planned for Wednesday.
Mr. Kerry’s committee must approve the treaty before the Senate can ratify it by the required two-thirds vote in the Senate — 67 votes. That figure would require support from at least eight Republicans.
Democrats hope to ratify the treaty before November’s congressional elections. Defeat would set back the Obama administration’s nuclear disarmament goals and efforts to improve relations with Russia.