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Iran appears to be winning the contest for influence in Iraq, where Iraqi Prime Minister Nouri al-Maliki’s Shiite-dominated government has consolidated power, and in Lebanon, where the Shiite militant group Hezbollah toppled the Saudi-backed government this year.

But the Saudi intervention in Bahrain has raised the specter that Saudi Arabia could assert itself more actively if it feels its vital interests are being threatened.

“What’s important is that the Saudis for the first time have put down red lines,” said Amos Yadlin, Israel’s former chief of military intelligence. “They say ‘OK, propaganda from Iran is fine, the intelligence war is fine, but if you’re going to change regimes in the Gulf, this is a red line.’ “

Although the U.S. accused Iran of trying to take advantage of unrest in Bahrain, it has stopped short of suggesting that the protesters are aligned with Iran. Officials say the protesters have legitimate grievances that the government needs to address through political reform.

“To date, I haven’t seen much evidence, if any, that the Iranians are terribly involved with Bahrain, but clearly that could change,” Ms. Maloney said. “Same is true for Yemen. And the Saudis are putting up a lot of cash in Egypt, looking to mold the future transition. You’re going to see a contest for influence that’s going to get very ugly in a lot of places.”

Mr. Jones, the Rutgers professor and author of “Desert Kingdom: How Oil and Water Forged Modern Saudi Arabia,” said he thinks an outright Saudi-Iranian military confrontation is unlikely, given the presence of U.S. and other international naval forces in the Persian Gulf.

However, he said he fears a scenario in which Iranian-sponsored terrorist attacks in the Gulf provoke a regional war that draws in the United States.

“I think the Saudis desire it,” he said. “If you watched Saudi TV coverage of this past week, they’ve been almost giddy because this vindicates their narrative about Iran.”