US President Barack Obama has urged both sides in Egypt not to use violence but has thrown his weight behind change.

"There are certain core values that we believe in as Americans that we believe are universal: freedom of speech, freedom of expression, people being able to use any social networking or any other mechanisms to communicate with each other and express their concerns. That is no less true in the Arab world than it is here in the US," the president said.

But he faces a dilemma - one other presidents have faced in South America, Asia and indeed the Arab world. Which are more important: timeless principles or reliable allies?

Egypt is important for the US. It is the guardian of the still critical Suez Canal and is the most populous country in the region. It was the first country in that part of the globe to make peace with Israel and, from the perspective of US policy makers, a force for moderation and reason.

It gets $1.5bn (£942m) in aid from the US, just behind Israel, Pakistan and Afghanistan. When Mr Obama wanted to send a message about a new beginning with the Muslim world, he chose to make his speech in Cairo.

There are those who think the administration's reaction to the street demonstrations is muddled, flimsy and uncertain. No doubt there is still a lot of internal debate.

But there is a response emerging, even if it is characterized by trepidation and wishful thinking. While Mr Obama's spokesman Robert Gibbs has said that Egyptian President Hosni Mubarak is a close and important partner, he has also said that President Obama has continually pressed for "political discourse".

Over at the US State Department, spokesman PJ Crowley said: "Reform is needed, no question about it". But what was really interesting was the analysis that followed.

"There's a regional dynamic... across the region from the Middle East to North Africa, countries do face similar demographic challenges - young populations, highly educated, very motivated, looking for jobs, looking for opportunities and quite honestly frustrated by, depending on the country, what they see as a lack of opportunity," Mr Crowley added.

So the State Department at least believes a wind of change is blowing through the top of Africa, and they don't want to be on the wrong side of history or indeed the wrong side of new rulers, who might turn out to be good friends if handled correctly. Clearly they are not going to be rude to an old ally, but nor are they going to place all their bets on the reforming instincts of an 83-year-old man, one who has resisted change for three decades.

But that brings us back to one of America's oldest problems. From the founding fathers onwards, there have always been Americans who hope their country's example would inspire others around the world to kick out tyrants and dictators and embrace democracy. And there have long been other Americans who think democracy is fine and dandy if it wasn't for pesky foreign voters going and choosing the wrong sort of people, who may not have the best interests of US policy makers in mind.

It used to be the communists they worried about, now it's the Islamists. The Center for American Security's Robert Kaplan pushes the case for realpolitik, explaining that "in terms of American interests and regional peace, there is plenty of peril in democracy".

"It was not democrats, but Arab autocrats, Anwar Sadat of Egypt and King Hussein of Jordan, who made peace with Israel. An autocrat firmly in charge can make concessions more easily than can a weak, elected leader. Just witness the fragility of Mahmoud Abbas's West Bank government. And it was democracy that brought the extremists of Hamas to power in Gaza," Mr Kaplan said.

After all, in Egypt, the best organised, biggest opposition movement is - despite being banned from open political activity - the Muslim Brotherhood. Some say they would easily win any free election in Egypt and they wouldn't exactly be the cosiest partner for Mr Obama and the US.

The National Review's summary may be close to the administration's view, if expressed in the rather more blunt language.