RIYADH, Saudi Arabia — Saudi Arabia and Iran are working together to try to calm the crises in Iraq and Lebanon, the Saudi foreign minister said yesterday, despite Washington’s efforts to isolate Tehran and limit its influence in the Middle East. The mediation is an unusual step by two rivals, Saudi Arabia and Iran, that compete for regional influence.

President Bush has rejected calls that America win Iran’s help in easing Iraq’s bloodshed and resolve the political crisis in Lebanon that erupted into violence last week. Instead, he has vowed to break what he called Iranian support for militants in both countries.

Saudi Arabia’s willingness to work with Iran likely indicates the growing alarm in the kingdom’s leadership over the two simultaneous crises, which have inflamed Sunni-Shiite tensions throughout the Middle East.

At the same time, Saudi Arabia has given tepid support to a new American strategy in Iraq but has expressed skepticism over whether it will succeed. Besides sending 21,000 additional American troops to Iraq, the new strategy takes a tougher stance on Iran.

Foreign Minister Saud al-Faisal of largely Sunni Saudi Arabia said yesterday that Iran had approached his country to “cooperate in averting strife between Sunnis and Shiites in Iraq and Lebanon.”