HONOLULU — Fortifying one of its key allies in the Persian Gulf, the Obama administration announced a weapons deal with Saudi Arabia on Thursday, saying it had agreed to sell F-15 fighter jets valued at nearly $30 billion to the Royal Saudi Air Force.

The agreement, and the administration’s parallel plans to press ahead with a nearly $11 billion arms deal for Iraq, despite rising political tensions there, is dramatic evidence of its determination to project American military influence in an oil-rich region shadowed by a threat from Iran.

Though the White House said the deal had not been accelerated to respond to threats by Iranian officials in recent days to shut off the Strait of Hormuz, its timing is laden with significance, as tensions with Iran have deepened and the United States has withdrawn its last soldiers from Iraq.

“This sale will send a strong message to countries in the region that the United States is committed to stability in the gulf and the broader Middle East,” said Andrew J. Shapiro, the assistant secretary of state for political-military affairs. “It will enhance Saudi Arabia’s ability to deter and defend against external threats to its sovereignty.”

The agreement also suggests that the United States and Saudi Arabia have moved beyond a bitter falling-out over the uprisings in the Arab world. Though the two countries continue to differ on how to handle the popular revolts in the region, American and Saudi officials said, the disagreement has not fractured a strategic alliance based on a common concern over Iran.

Saudi Arabia is a longtime foe of Iran, with relations souring further last fall after the United States broke up what it said was an Iranian-backed plot to kill the Saudi ambassador to Washington. Iran has denied the accusations.

“When you look at the size of this package, what does it tell you about U.S.-Saudi relations?” said a senior Saudi official, who spoke anonymously because he was not authorized to speak publicly. “It says it’s very strong and very solid. Any disagreements from time to time don’t affect the core relationship.”

The weapons package is remarkable, both for its size and for its technical sophistication. Under the terms of the $29.4 billion agreement signed on Dec. 24, Saudi Arabia will get 84 new F-15SA jets, manufactured by Boeing, and upgrades to 70 F-15s in the Saudi fleet with new munitions and spare parts. It will also get help with training, logistics and maintenance.

The new F-15s, which will be delivered in 2015, are among the most capable and versatile fighter jets in the world, Pentagon officials said. They will come with the latest air-to-air missiles and precision-guided air-to-ground missiles, enabling them to strike ships and radar facilities day or night and in any weather.

Though Mr. Shapiro and other officials said the planes were intended to help Saudi Arabia protect its sovereignty, military analysts said they would be effective against Iranian planes and ships anywhere in the Persian Gulf. They are part of a 10-year, $60 billion weapons package for Saudi Arabia that was approved last year by Congress.

At the time, there was a vigorous debate, with some lawmakers arguing that such a huge arms package would threaten the military position of Israel. Mr. Shapiro, speaking at a State Department briefing, said the administration was satisfied that the sale of the F-15s would not diminish “Israel’s qualitative military edge.”

The White House portrayed the arms sale as part of a concerted effort to shore up its relationship with Saudi Arabia. President Obama has made several telephone calls to King Abdullah, a senior official said; the national security adviser, Thomas E. Donilon, traveled twice to the Saudi capital, Riyadh; and Vice President Joseph R. Biden Jr. led a high-level delegation to the funeral of Crown Prince Sultan bin Abdul Aziz in October.

Early this year, the Saudis were furious when Mr. Obama withdrew support for Egypt’s embattled president, Hosni Mubarak, after he faced massive protests in Cairo’s Tahrir Square. Later, it was the White House’s turn to be upset, when Saudi tanks rolled into neighboring Bahrain to help quash a mainly Shiite rebellion against that kingdom’s Sunni monarchy.

Yet Saudi Arabia and the United States continue to cooperate in areas like counterterrorism. In recent weeks, the two have worked to resolve the crisis in Yemen, where President Ali Abdullah Saleh has formally agreed to cede power in a Saudi-brokered agreement and has applied for a visa to travel to the United States for medical treatment.

“The agreement reinforces the strong and enduring relationship between the United States and Saudi Arabia,” Joshua R. Earnest, the White House’s deputy press secretary, said in a statement issued in Hawaii, where Mr. Obama is on vacation.

With the United States pulling out of Iraq, the administration has been eager to demonstrate that it will remain a presence in the region. It is proceeding with weapons sales to Iraq, despite fears that Prime Minister Nuri Kamal al-Maliki may abandon his American-backed power-sharing government in favor of a Shiite-dominated state.

The administration has weighed stationing combat troops in Kuwait in case of a military confrontation with Iran or a collapse in security in Iraq. It is also seeking to expand military ties with other gulf countries, including Qatar, Oman and the United Arab Emirates.

“I see this more in the longer-term effort by the administration to signal that even with the withdrawal of troops from Iraq, the U.S. is still committed to the defense of its allies in the gulf and to the containment of Iran,” said F. Gregory Gause III, an expert on Saudi affairs at the University of Vermont.

The weapons deal, Mr. Gause said, also illustrated that the two countries could put aside their differences and focus on larger strategic priorities. “After some tension-filled months this year over Egypt and Bahrain, both sides have agreed to disagree on that, and agree on their common interests,” he said.

NYT