The Obama administration is committed to preventing Iran from obtaining nuclear arms as a “vital national security interest” but believes there is still time to change Iranian behavior through economic and political pressure, a former top adviser on the Middle East said Tuesday.

Dennis Ross, who stepped down last month as special assistant to President Obama, portrayed Iran as behind schedule on its nuclear program and battered by some of the worst strain seen in the country in three decades. Yet, more pressure is needed to prevent its leaders from acquiring a nuclear capability that would destabilize the region and heighten the risk of war, he said.

“This is not about containment; it’s about prevention,” Ross said in his first public address since leaving the White House. “I believe we still have time and space to achieve that objective.”

Ross made the comment during a wide-ranging speech, in which he also played down chances for a breakthrough on Middle East peace in the near future and gave a cautious assessment of the recent gains by Islamist parties in Arab countries that have overthrown autocrats.

He cited a “huge gap, psychologically,” between Israeli and Palestinian leaders and conceded there was “not a high prospect” of achieving a comprehensive peace settlement soon. While declining to ascribe blame for the impasse, he warned that it would be a mistake for Israeli leaders to wait until the current Middle East tumult subsides before pursuing peace.

“There are many in Israel who look at the region and say, ‘Now is not the time,’ ” Ross told a gathering at the Washington Institute for Near East Policy, a think tank to which he returned after quitting his government job. “If you sit back and wait for things to clarify, you will be acted upon. Your options shrink; they don’t expand.”

Ross, who counseled five U.S. administrations on Middle East policy, was the second top adviser on the region to leave the Obama administration this year, his resignation coming six months after former senator George J. Mitchell Jr. (D-Maine) quit as White House special envoy on Middle East peace. Ross said in his speech that his departure was for personal reasons and not spurred by policy disagreements or frustrations over the lack of progress in peace talks.

While acknowledging difficulties in the administration’s relations with the government of Israeli Prime Minister Benjamin Netanyahu in the past three years, Ross said that ties between the two countries were “solid.” He said both shared essentially the same assessment of the threat posed by Iran.

Ross said a nuclear-armed Iran would pose an existential threat to Israel and a “most profound danger” to vital U.S. interests by dramatically increasing the risk of a destabilizing war.

Yet, while asserting that Iran is “undeniably” making progress toward a nuclear-weapons capability, Ross suggested that economic pressures and technical problems inside Iran had bought additional time for the West.

He noted that Iran’s nuclear efforts had fallen far short of the timetables set by the country’s leaders a few years ago. Hampered by a cyberattack and other woes, Iran is known to have only about 6,000 working centrifuges, and the average performance of the machines has been declining.

“Ratcheting up the pressure continues to be the answer,” Ross said. But he added: “We’re not quite there yet.”