Both are clerics with strong revolutionary credentials and scant affection for the West. Both describe themselves as the natural political heirs of Iran's popular outgoing president, Ali Akbar Hashemi Rafsanjani. Both are 54. But there are important differences between Ali Akbar Nateq-Nouri and Mohammed Khatemi, the front-runners in today's presidential election _ the seventh and most competitive such contest since the Islamic revolution in 1979. Nateq-Nouri, the speaker of Iran's parliament, is an arch-conservative who last year described the United States as a "blood-sucking wolf" and recently found it necessary to deny rumors that he would require schoolgirls to wear the tent-like black robe known as the chador. Khatemi is a scholar and educator who heads the national library. He lost his job as minister of culture and Islamic guidance several years ago because he was seen as too permissive. Although Nateq-Nouri was once seen as a shoo-in, given his close ties to Iran's all-powerful religious establishment and the backing of supreme leader Ayatollah Ali Khameini, the race has tightened in recent weeks. That has generated excitement among Iranians fed up with the failure of their clerical leaders to root out corruption and deliver on promises of jobs and prosperity. While a Khatemi victory would be unlikely to temper Iranian hostility toward the West, at least in the short term, it almost certainly would usher in an era of greater political pluralism and social and cultural freedom, in the view of foreign diplomats and Iranian political analysts. "If Khatemi wins, things will become more interesting, partly because he is known to be more open-minded and partly because it will be seen as evidence that the system hasn't got everything its own way," a Western envoy said. The race has been a rough and tumble one, featuring widespread vandalism of campaign posters and a hearty dose of negative campaigning, especially in the Nateq-Nouri camp, which accuses Khatemi of being a liberal who secretly wants warmer relations with the United States. Khatemi has been drawing large and enthusiastic crowds, particularly in Tehran, where he is enormously popular among students and poor people wooed by his liberal economic agenda. "He's a moderate and he's going to develop the country toward the West," Moshallah Zadeh, 25, a university student, shouted above the din of an exuberant mob of 5,000 or more who turned out to hear him speak at a mosque in east Tehran on Wednesday night. "He's going to guarantee that we'll have freedom of thought." Iranian democracy has its limits. Candidates are screened for ideological purity by the Council of Guardians, a conservative clerical body that has the power to cancel election results without explanation. The council rejected all but four of 238 presidential candidates; the other two do not have a serious chance of winning. If no candidate wins an outright majority, the contest will be decided in a runoff. Whoever does get elected will be subordinate to Khameini and, for that matter, Rafsanjani, who will take over as head of a newly expanded consultative body called the Assembly for Diagnosing the Interests of the Regime.