TEHRAN, June 11 (AFP) - Iran's reformist President Mohammad Khatami has swept to a landslide re-election victory, as voters dealt a crushing blow to hardliners' efforts to block his bid to reform the Islamic republic.

"The nation has strived to present a right and just model of a civil society based on religion and morality alongside democracy and freedom," a soft-spoken Khatami said after his win of 77 percent of votes was announced.

He said he would attempt to instill "a legal, healthy and open atmosphere, freedom of speech and criticism and even opposition within the framework of the law," an agenda that has for the past four years met stiff and often brutal resistance.

"This is a real victory, and paying this great nation back will not be easy for the one they have supported," said the moderate cleric, who is set for his second and final term to implement the most ambitious reforms in the 22-year-old history of the Islamic republic.

Final results announced overnight Saturday gave Khatami a staggering 77 percent of the vote, as Iranians emphatically rejected conservatives linked to an un-elected religious hierarchy fighting to retain its virtual monopoly on power.

The interior ministry said Khatami won more than 21.6 million out of 28.1 million votes cast on Friday, leaving even the closest of the nine runners-up, conservative Ahmad Tavkaoli, well behind at 15.6 percent.

Seven of the other eight candidates were humiliated, failing to pass the one percent mark -- signalling the failure of a conservative tactic to erode Khatami's popular support.

But when the ministry announced the result overnight Saturday, it made a radical downward revision of turnout figures, saying just 67 percent of eligible voters cast their ballots Friday after reporting earlier that 83 percent had done so.

No explanation for the change was given.

But since there were six million more eligible voters on Friday than in 1997 -- when Khatami won around 20 million votes in a turnout of 83 percent -- conservatives could now assert that in real terms his support has dropped.

The result also still has to be rubber-stamped by the conservative Guardian Council. Their decision is expected in the coming days.

The figures nevertheless confirmed that Khatami is a powerful force to be reckoned with, setting the stage for another political battle with establishment hardliners who claim his reforms are leading the nation to ruin.

The 57-year-old former culture minister, a hero to many in a nation where young people make up two-thirds of the population, has eased social pressures at home while working to restore Iran's image on the international stage.

He drew the world's attention to his struggle when he broke down in public last month, wiping tears from his eyes as he described the "heavy price" paid by his reform movement.

Newspapers which flourished under his first tenure were shut down wholesale by the courts, which locked dozens of reformists -- from ageing opposition figures to young students thirsting for change -- away in prison.

Khatami believes the nation is ready for an "Islamic democracy" that combines the state religion with Western-inspired rights and freedoms. Many conservatives see that as "Westoxication."

They also see their own popular support ebbing after 22 years of clerical rule, and supreme leader Ayatollah Ali Khamenei, the number one figure in the regime, preferred to hail the vote as support for the regime as well as the constitution -- the document which gives him virtually unlimited power.

Former president and prominent conservative, Ali Akbar Hashemi-Rafsanjani, for his part sent a message reminding Khatami of his commitments to the clerical regime.

"With such a popular trust and support, I hope that you will successfully serve the people and fulfil the objectives of the holy Islamic system," Rafsanjani wrote.

Friday's vote marked the fourth consecutive win for reformists, after similar crushing victories in municipal and parliamentary polls in 1999 and 2000, and Khatami's initial 1997 election.

Victory celebrations, however, quickly gave way to cautious optimism, among foreign diplomats and Iranians alike.

"Can he deliver?" asked a senior Tehran-based European diplomat. "There is a huge mandate, but that also means huge aspirations."

While he may be pushing for freedoms, Khatami is also under fierce pressure to turn around a stagnant economy lumbering under 80 percent state control.

"What is certain is that Khatami will have problems," said Shahrdad Rahmanifard, professor of political science at Tehran's Free Islamic University.

"He cannot go too fast: this is still a traditional Muslim country, and he is walking on a razor blade."