Rice, on a tour of the region, told an audience of 700 invited government officials, academics and students at the American University in Cairo on Monday that Washington was serious about supporting democracy in the region.
"Millions of people are demanding freedom for themselves and democracy for their countries. To these courageous men and women, I say today: All free nations will stand with you as you secure the blessings of your own liberty," she said in an address aired live on the Arab television stations.
Rice arrived in the Saudi capital of Riyadh later during the day.
She criticised Saudi Arabia's record on democratic reform and the jailing of three activists.
But her calls for democratic reforms in the Middle East were met with a fair degree of scepticism in the Arab world, and a rebuff from the Saudis.
"The row is really meaningless," Saudi Foreign Minister Prince Saud al-Faisal told a post-midnight news conference after Rice conferred with him and the country's de facto ruler, Crown Prince Abdullah bin Abdulaziz.
"The assessment that is important for any country in the development of its political reform is the judgment of its own people," Saud said. "And that is, in the final analysis, the criteria that we follow."
Rice met Egyptian opposition
leader Ayman Nour among others
Some suspect US motives, and others feel Washington will not really press its top allies to loosen their hold on power. But a few say the fact that Rice criticised autocratic practices on their soil was a sign that things are different.
In Cairo, Rice met privately with a handful of Egyptian reformers - both in opposition and in the ruling party.
Ayman Nour, an opposition leader who spent 45 minutes with Rice, said some participants had told her US calls for reform must be tied to American policy.
"This [reform] project will not have any credibility without a full withdrawal from Iraq, without a withdrawal from Gaza, and without a return to the road map [peace plan for the Palestinians and Israelis]," Nour said.
In downtown Cairo, a few dozen protesters gathered in front of Cairo's High Court to denounce Rice's visit.
"Down, down America!" they shouted.
Egypt's strongest opposition movement, the outlawed Muslim Brotherhood, said the US was in no position to spearhead calls for reform in the region.
There is "a clear contradiction between the US calls for democracy, good governance and human rights and its invasion of Afghanistan, occupation of Iraq, support for Israel and abuses at Guantanamo Bay and Abu Ghraib", the Brotherhood's deputy leader, Mohammed Habib, said.
He added his group was not invited to meet Rice.
A Saudi dissident living in London said American interests in his homeland - primarily oil and fighting "terrorism" - stand in the way of serious pressure on his government for change.
"Millions of people are demanding freedom for themselves and democracy for their countries. To these courageous men and women, I say today: All free nations will stand with you as you secure the blessings of
your own liberty"
US secretary of state
"Beyond that, they do not care," Abdul Aziz Khamis said of Americans in a telephone interview. "Some American officials say something, but do something else. They want to make a better image for the ugly reality."
One of Egypt's most vocal reform movements, Kifaya, declined to attend Rice's lecture in Cairo, saying they see the US administration as wooing the Egyptian government.
"The main streak of US policy so far has been supportive of the Egyptian government," said Abdel Halim Qandil, a leading member of Kifaya, which has staged unprecedented demonstrations against the government in the past seven months.
But some saw Rice's visit as opening a new page.
Naguib Sawiris, Egypt's most prominent businessman, who attended the lecture, said: "I think her visit makes a difference because we hear it here on the Egyptian soil and she had an opportunity now to discuss with various Egyptians and [hear] their questions."