Thousands of Iranians gathered at the late Ayatollah Ruhollah Khomeini's tomb Thursday, the 11th anniversary of his return from exile, and his son preached continued hostility to America, Tehran radio said. On the first anniversary since the revolutionary patriarch's death June 3, Ahmad Khomeini said his father, known as the Imam, constantly defied ``global arrogance,'' an Iranian phrase for United States and its allies. ``We must always remain on the Imam's path,'' he said at a ceremony beginning a 10-day celebration of the Islamic revolution. Ahmad Khomeini said his father warned that, ``if we show the slightest bit of complacency, America will deliver its final blow against us. You, the people, must prepare for struggle against America.'' The radio the younger Khomeini, a leading radical, praised his father's successor as spiritual leader, Ayatollah Ali Khamenei, for ``treading the same path as the Imam.'' His exhortation for no compromise with the United States was seen as a warning to President Hashemi Rafsanjani, leader of the so-called pragmatist faction in Iran. Rafsanjani, who attended the ceremony Khomeini's golden-domed tomb in the Behesht Zahra cemetery, seeks better relations with the West in order to obtain help in recovering from eight years of war with Iraq. The first part of Rafsanjani's 5-year development plan, calling for up to $20 billion in foreign investment, got Parliament's approval Wednesday over opposition from radicals who want state control and no foreign involvement. Tehran television showed throngs at the cemetery chanting ``Death to America!'' and ``Death to Israel!'' Iranian officials paid their respects at the tomb and promised to safeguard Khomeini's ideological legacy, the radio said. ``At a time when the government was in the hands of the enemy, the Imam's coming from a safe place to the center of the danger was an act rooted in the immense power of the Lord,'' Rafsanjani said at the graveside, the radio reported. Khomeini returned from 14 years of exile Feb. 1, 1979, after Shah Mohammad Reza Pahlavi was forced to flee. Ten days later, the government he left behind collapsed and Khomeini proclaimed the Islamic republic, Rafsanjani said: ``The Iranian people have proved that if a nation is resolute in its stand, and if it has courage and spirit, it cannot be defeated.'' He said recent changes in Eastern Europe and elsewhere were ``a small example of what the people of Iran achieved 11 years ago, and these popular rebellions are the legacy of the people of Iran.'' Khamenei, the nation's spiritual leader, told another gathering in Tehran: ``The future belongs to Islam, the Moslems and the freedom-loving nations of the world,'' the television reported. ``In the confrontation with the organizations of the satanic powers (the West), it will be Islam which triumphs.'' Despite the fiery rhetoric, this year's anniversary of the revolution differs from past observances. It reflects the more more relaxed character of Rafsanjani's government, formed in August, and an easing of Islamic rigidity. While Khomeini was alive, the anniversary was a time of rallies to show support for him, and of reruns on state television of bloody clashes between revolutionary zealots and the shah's forces. On Thursday, television showed film of Khomeini arriving in Tehran in 1979 on a chartered Air France jet, but comedy and children's shows dominated the morning programming. The official Islamic Republic News Agency said music would be part of the celebrations this year for the first time. Khomeini felt good Moslems should shun music.