Themalevolent face of Assadollah Lajevardi, the new director-general of Iran's prisons, says it all about human rights in Iran. They don't exist.

President Hashemi Rafsanjani has appointed this man, whose reputation as the top torturer of Tehran is uncontested. Lajevardi should have been tried or at least banished for his bloody excesses during the reign of the Ayatollah Khomeini. Instead, he is overseeing all prisons in Iran, proving that Khomeini's death and Rafsanjani's ascension to power changed nothing.

This week, a United Nations team will be allowed into Iran's prisons to investigate allegations of human rights abuses. Rafsanjani, who authorized the investigation as a public relations tool, now has just cause to be anxious, especially with Lajevardi at the helm.

Lajevardi is widely known in Iran as the ''Butcher of Evin'' -- a nickname earned when he presided over Iran's most notorious prison, Evin, in the foothills outside Tehran. It is one of 70 prisons in and around Tehran alone and one of 600 throughout Iran.

A former lingerie peddler, Lajevardi took to the Evin assignment like a rattlesnake takes to exposed flesh. He packed 60 prisoners to a cell at Evin, executed thousands and tortured thousands more in ways that normal people could not conceive.

He and other officials, including a member of the Iranian parliament, raped female prisoners, including virgins whom Khomeini wanted sullied before they were sent to the next life.

The innovation that earned Lajevardi the ''butcher'' nickname was his practice of draining the blood of Iranians on death row. The blood was used as plasma for Iranian soldiers fighting the long war with Iraq. Lajevardi was careful to leave his victims just enough blood so they were conscious when they went before the firing squad.

As an exterminator, Lajevardi takes his philosophy from Adolf Hitler and Josef Stalin. He once called Stalin a ''godless idiot who killed 60 million people in the service of his stupid socialism.'' Then he added, ''Isn't Islam worthy of a similar tribute to its grandeur?''

Small wonder that the United Nations suspects that Rafsanjani is no more moderate than his madman predecessor. Our sources in Iran and in the U.S. intelligence community say that about the only difference between Rafsanjani and Khomeini is that Rafsanjani is more interested in better relations with the West.

That may explain why Rafsanjani has allowed the United Nations to send an investigator to the prisons. For eight years, the U.N. Human Rights Commission has condemned Iran for its abuses, and the U.N. General Assembly has concurred in the past five years. All the reports were made without benefit of an on-site investigation, because Khomeini wouldn't allow it.

In 1988, Iran's U.N. ambassador, Jaafar Mahallati, agreed to an investigation and then withdrew the invitation when the United Nations adopted a resolution critical of Iran. (Mahallati was later recalled to Iran for paying too much attention to human rights and was secretly tortured at Khomeini's order. He suffered a heart attack during the torture but survived.)

The new Iranian representative to the United Nations, Kamal Kharrazi, surprised the secretary general by agreeing in writing to an investigation. A committee of the U.N. General Assembly then dropped a resolution that was critical of Iran's human rights record and approved a statement welcoming the decision to admit U.N. investigators.

The leader of the U.N. delegation to Iran this week is no pushover. He is Reynaldo Galindo Pohl, a Salvadoran who will not be easily blinded by the dog and pony show that Rafsanjani and Lajevardi will stage.

There are clues that Rafsanjani is already beginning to regret his invitation. He has imposed a press blackout so the people of Iran do not know about the visit and hence will not go out of their way to talk to the U.N. representatives.