DOHA, Qatar  Secretary of State Hillary Rodham Clinton delivered a scalding critique of Arab leaders here on Thursday, saying their countries risked “sinking into the sand” of unrest and extremism unless they liberalized their political systems and cleaned up their economies.

Speaking at a conference in this gleaming Persian Gulf emirate, Mrs. Clinton recited a familiar litany of ills: corruption, repression and a lack of rights for women and religious minorities. But her remarks were striking for their vehemence, and they suggested a frustration that the Obama administration’s message to the Arab world had not gotten through.

“In too many places, in too many ways, the region’s foundations are sinking into the sand,” she said to a stone-faced audience of foreign ministers, businesspeople and rights groups. “The new and dynamic Middle East that I have seen needs firmer ground if it is to take root and grow everywhere.”

Mrs. Clinton’s remarks were delivered at the end of an intense, four-day tour of the Persian Gulf that took her from impoverished, autocratic Yemen to the prosperous, comparatively open sultanate of Oman. She also stopped in Abu Dhabi and Dubai before finishing in Qatar, a wealthy fief still exulting in its selection as the site of the World Cup soccer tournament in 2022.