U.S. Defense Secretary Robert Gates arrived in Cairo today on his first visit to Egypt since opposition demonstrators ousted President Hosni Mubarak and a military council began a transition of power.

The unannounced visit will include meetings with Prime Minister Essam Sharaf and Army Field Marshal Mohammed Hussein Tantawi, whose more than half-dozen telephone calls with Gates helped keep the Obama administration informed of developments during the turmoil.

Gates “has gotten to know Field Marshal Tantawi very well over the past several years and especially well over the past couple of months,” the Pentagon spokesman, Geoff Morrell, told reporters traveling with Gates. “He is especially appreciative of his leadership and the performance of his military during a very tumultuous period in Egypt.”

Gates’s visit follows one by Secretary of State Hillary Clinton as the administration strives to maintain continuity in a relationship anchored by Egypt’s peace treaty with Israel and $1.3 billion a year from the U.S. in military aid.

The U.S. sees the defense ties as having paid off during the revolt against Mubarak’s 30-year rule. Close coordination in the past on regional security issues such as terrorism and threats to Israel, as well as extensive training, exercises and professional exchanges between the two militaries, kept the lines of communication open amid the upheaval of recent months.

Gates aims to reaffirm those ties, discuss a recent constitutional referendum in Egypt and get the two leaders’ views on the popular revolts rocking the Middle East.

Attacks on Libya

The discussions will include the attacks by the U.S. and its partners on air defenses in neighboring Libya to stop Colonel Muammar Qaddafi’s forces from targeting his opponents.

Voters in Egypt’s first referendum since Mubarak’s Feb. 11 ouster backed a set of constitutional changes that some critics say may favor established groups such as the Muslim Brotherhood in future elections.

More than 18 million valid ballots were counted, with 77.2 percent of voters approving the changes, according to the judicial commission overseeing the referendum.

Gates is “very encouraged, especially coming out of this successful referendum, that Egypt is trending in the right direction as it transforms itself into a democratic, civilian- led government,” Morrell said.