Clinton was the highest-ranking Obama administration official to visit Tunisia and Egypt since popular uprisings there forced out longtime leaders in January and February. Her Mideast trip was overshadowed by the violent flip side of changes sweeping the Arab world, as a crackdown intensified in U.S.-allied Bahrain and rebels fell back in their attempt to unseat Libyan strongman Moammar Gadhafi.

Clinton pledged U.S. support as the two countries embark on the difficult transition to democracy, including elections in the summer. Washington is offering aid packages that include investment credits, loan guarantees, insurance as well as public private partnerships in the fields of education, technology and science.

In a Tunis town hall meeting at the end of her trip Thursday, Clinton praised the popular uprising that ousted longtime ruler Zine El Abidine Ben Ali in mid-January, after a month of street protests. The revolt quickly spread across the Arab world, toppling Egyptian President Hosni Mubarak and challenging the rule of leaders elsewhere in the region.

"You have seen the contagion. It's the Tunisian contagion. It is a good kind of contagion," Clinton told an audience of several dozen students, business people and civic leaders.

"I had no idea that Tunisia would alight this awakening," she said. "The revolution here has begun the democratic transformation (around the region) and it is my great hope that Tunisia will be the model democracy for the 21st century."

The popular protests initially caught the U.S. in a bind since they targeted many traditional U.S. allies in the region, including Mubarak. However, the Obama administration quickly came to support the pro-democracy rallies and this week warned the ruler of Bahrain, a key ally, against a violent crackdown.