WASHINGTON  With tensions over Iran’s nuclear ambitions hitting new levels, the United States is mounting a diplomatic full-court press in the Middle East, sending four top diplomats, including Secretary of State Hillary Rodham Clinton, to confer with Arab and Israeli leaders.

The envoys’ visits to Israel, Lebanon, Syria, Jordan, Egypt, Saudi Arabia and Qatar were planned separately in recent weeks, but they now have a common purpose, administration officials said: to reassure Iran’s neighbors that the United States will stand firm against Tehran, and to enlist other countries in a global effort to put pressure on the Iranian authorities.

Mrs. Clinton will play a central part in the effort, leaving Saturday for Qatar and Saudi Arabia, where she will meet with the Saudi leader, King Abdullah. Officials said she was expected to press the Saudis to reassure China that Saudi Arabia would offset any disruption in oil shipments that could occur if Beijing were to back new United Nations sanctions against Iran.

China, which has major investments in Iran’s oil and gas industry, has been the main holdout in the American-led effort to impose tougher sanctions against Iran through the United Nations Security Council.