Defense Secretary Leon E. Panetta sought Sunday to portray the United States and Israel as unified in their support for increasingly tough international sanctions, rather than military measures, against Iran to prevent it from developing a nuclear weapon.

Although top Israeli officials have said repeatedly that the economic sanctions are not slowing the Iranian program, Panetta played down the possibility of an Israeli strike in the near term. “My view is that they have not made any decisions with regards to Iran and they continue to support the international effort to bring pressure against Iran,” he said of Israel.

Panetta is to arrive in Israel on Tuesday, just days after a visit by Republican presidential candidate Mitt Romney, whose campaign has tried to suggest that the Obama administration is not sufficiently supportive of Israel. The administration has sought to portray its relationship with the Jewish state as strong.

The defense secretary’s trip follows a flurry of visits from top administration officials to highlight the two countries’ mutual resolve to thwart Iran’s nuclear ambitions.

Panetta maintained that increasingly tough economic sanctions are weakening Iran’s resolve to sustain its nuclear program and should be given more time. “The sanctions in these next few weeks are going to be ratcheting up to a whole new level of impact,” he said. “It is basically sending a very strong message to [the Iranians] that they can’t continue to do what they are doing.”

The Romney campaign has sought to differentiate the candidate from President Obama by suggesting that the former Massachusetts governor would not try to stop Israel from striking Iran to prevent it from acquiring a nuclear weapon. “If Israel has to take action on its own in order to stop Iran from developing that capability, the governor would respect that decision,” said Dan Senor, a senior foreign policy adviser.

Panetta relayed a similar message regarding Israel, even as he emphasized his belief that the sanctions and increased diplomatic pressure offer the best opportunity to squelch Iran’s nuclear program. “We respect [Israel’s] sovereignty and their ability to make decisions with regard to their own security,” he said.

Although U.S. and Israeli intelligence assessments of Iran’s nuclear program have differed in the past, the two countries have in recent months agreed about its status.

Panetta’s trip to Israel is part of a five-day swing that includes stops in Tunisia, Egypt and Jordan.

In addition to growing concerns about Iran, the trip will be dominated by the worsening bloodshed in Syria, where President Bashar al-Assad’s forces have mounted a major assault on Aleppo, the country’s largest city. In Israel and Jordan, Panetta is expected to discuss the status of Syria’s chemical and biological weapons stockpiles and the need to secure them amid the growing chaos.

The Syrian leader has managed to hold onto power for 16 months even as rebel fighters in recent months have gained control of significant swaths of the country. ­Panetta said that the indiscriminate violence in Aleppo would be “a nail in Assad’s coffin.”

Tunisia, the defense secretary’s first stop, is where the uprisings known as the Arab Spring began in December 2010 and where a new government is expected to ask for U.S. assistance in securing its borders and dealing with the threat posed by al-Qaeda and its offshoots in northern Africa.