WASHINGTON — Wrapping up the annual American Israel Public Affairs Committee conference, Defense Secretary Leon Panetta and three of the four top GOP candidates will address the conference’s 13,000 delegates.

This will mark the first time that a sitting U.S. president and  secretary of defense will appear at the same AIPAC conference. Panetta’s speech will likely address Iran’s nuclear program and emphasize the success of the recently intensified Iranian sanctions. His speech is also expected to attempt to quell skepticism from conference delegates, who have been disappointed by the Obama administration.

This year’s conference is also the first time presidential candidates from the opposing party will speak during a year when the incumbent is seeking reelection.

Republican presidential candidates Mitt Romney and Newt Gingrich will speak via satellite from the campaign trail on Super Tuesday, while Rick Santorum will speak in person. The three frontrunners are expected to criticize President Barack Obama for not doing enough to prevent Iran from building nuclear weapons.

AIPAC refused to invite Rep. Ron Paul to speak because of his voting record against U.S. assistance for Israel and past instances of anti-Israel rhetoric.

The three-day event will end later today when thousands of people descend on Capitol Hill to lobby for financial and military aid to Israel.