-- It was almost a perfect crime. Three well-dressed men walked into the suburban compound of Iranian exile Shahpour Bakhtiar in broad daylight, passing through X-rays and metal detectors manned by 24-hour police guards, to slit his throat and disappear.


At first, it appeared a brilliantly plotted conspiracy, aided by luck. Then came the mistakes -- mistakes which three years later have not only led to the capture of key suspects in the case but have also produced a windfall of Iranian spy data for Western intelligence agencies.


In a trial that opened Wednesday in Paris under massive security, three suspects share the defense dock with the shadow of the state of Iran -- all accused by French investigators of playing a direct role in planning and carrying out the political assassination of Bakhtiar, a former Iranian prime minister.


What began as a murder case has unveiled the shape of what investigators regard as a surprisingly sophisticated Iranian intelligence and terror network that stretches from Europe to California.


French authorities report that:


?Southern California, a region with an Iranian community numbering over 500,000 people by several estimates, "is an operational base" of VEVAK, Iran's state intelligence and security agency.


?Iran's young, KGB-model spy network is now able to carry out its own assassination missions, rather than farming out such assignments to less disciplined terrorist groups; and,


?Secret agents of the Iranian government have infiltrated opposition and exile groups in Europe, the Middle East and California, often targeting their leaders for assassination.


"Iran seems to regard political assassination as its national right, even on foreign soil. Any country that enforces its laws against murder is seen interfering in the sovereign affairs of Iran," said one high-ranking French justice official.


Iran strongly denies the allegations. In an interview, Iranian Ambassador to France Hamid Asefi said that Bakhtiar posed no threat to Iranian security, and that Iran had no role in his death.


"Moreover, we deplore any such act of violence against any resistance group," Asefi added.


In unraveling the mystery of who killed Bakhtiar and pursuing the primary suspects in a network of perhaps 100 major and minor accomplices, French investigators were led on detective hunts to Switzerland, Turkey, Britain and the United States.


Results of that search are contained in a 185-page report obtained by the Los Angeles Times. It lays out a case that French journalists call "an autopsy of Iran's terror network."


That network, French investigators say, includes operatives in the U.S. In January 1993 a team of French police investigators followed their trail of conspiracy leads to Los Angeles, looking for possible suspects in the logistical support of the killers. They took testimony from one Iranian exile who denied any involvement but said he had been solicited to kill Bakhtiar by Iranian intelligence agents two years earlier.


But the French team was frustrated, in part because the U.S. attorney's office in Los Angeles, citing inadequate probable cause, refused to issue an arrest warrant requested by the investigators and turned down another request for a search warrant.


A U.S. Justice Department spokesman would not comment on the case except to say: "We cooperate and assist foreign law enforcement investigations in the United States aggressively and to the fullest extent permitted by our laws and procedures."


However, one French investigator said: "We told them (U.S. officials) there is a network of terrorists operating in your country. The Americans seemed to resent being told." Ironically, a month later terrorists attacked the World Trade Center in New York. The French had no advance knowledge of that plot. "But we delivered the earlier wake-up call," the French investigator said.