Mr. Clinton arrived early in Aspen. He was expected to stay through Sunday afternoon to help with a fundraising conference there, but changed his plans after the death of Hassan.
Mr. Clinton is returning to Washington Saturday, refueling, then flying to Morocco for SundayÂ's funeral.
Hassan, a longtime friend of the United States, died of a heart attack Friday in the Moroccan capital of Rabat. He was 70.
For more than a quarter-century, Hassan promoted reconciliation.
The president offered his condolences in a telephone call to Hassan's son and successor, Crown Prince Sidi Mohamed, then issued a statement lauding the late king.
"The Middle East has lost one of its greatest peacemakers," Mr. Clinton said. "He worked to break down barriers among the peoples of the Middle East, bravely opening a dialogue with Israel, ... seeking greater tolerance and stability in the region."
The king, sometimes covertly, promoted reconciliation between Israel and its Arab neighbors for more than a quarter-century. Israel's new prime minister, Ehud Barak, was planning a trip to Morocco in August and was sure to look to Hassan to reinforce his overtures to the Arabs.
U.S. Secretary of State Madeleine Albright also telephoned the crown prince from Tokyo, where she was en route to Singapore for a meeting of Asian leaders.
She said Hassan was "a pioneer of the Middle East peace process and an Islamic leader who was an enlightened promoter of religious tolerance and understanding."
Mohamed, the new monarch, offered Albright assurances that the United States could continue to rely on Morocco, said an administration official accompanying the secretary.
"We do expect continuity, especially in terms of going forth with the Mideast peace process," said the official, speaking on condition of anonymity. He described the new king as "quite bright, with a reformist bent."
Hassan's death follows the death of another prominent Arab moderate, King Hussein of Jordan. Both sought to promote peace in the region and supported Mr. Clinton's efforts to arrange a settlement.
The administration hopes their successors, King Abdullah II in Jordan and Mohamed in Morocco, will follow the policies of their fathers.
Until Egypt made peace with Israel in 1979, Morocco was the major Arab bridge between the U.S. and Israel's neighbors. Israel maintains a liaison office in Rabat, one level below an embassy, and had friendly relations with Hassan. His father, Mohamed V, protected the country's Jews from the reach of the Nazi Holocaust in World War II.