One hundred sixty-two House members assailed the Iranian government this week, saying the April assassination of an opposition leader in Switzerland proves terrorism is still an "indispensable pillar" of Tehran's foreign policy.

The accusations were in a letter sponsored by Rep. Mervyn M. Dymally (D-Calif.), and sent Tuesday to Massoud Rajavi, head of the Iraq-based National Council of Resistance and his organization, the People's Mojahedin.

His brother, Kazem Rajavi, 56, was gunned down April 24, authorities said, by a four-man assassination squad that stopped his car near his home in a Geneva suburb where he was a Mojahedin human rights lobbyist.

Swiss investigating magistrates recently reported that "one or more official Iranian agencies were directly involved in the assassination." They said there was evidence that 13 persons, all with Iranian government service passports, played roles in the "minutely planned" killing.

Dymally, chairman of the House Foreign Affairs subcommittee on international operations, said 99 Democrats and 62 Republicans signed his letter, which voiced support for the resistance's "peaceful and democratic aims."

A spokesman for the Iranian United Nations Mission in New York, Ramin Rafi, denounced the letter, calling the signers "tools of a terrorist organization."

Dymally's press secretary, Marwan Burgan, refused to disclose those who signed. Dymally did not return phone calls.

Iranian officials have denied involvement in the Rajavi assassination. Rafi blamed it on Mojahedin "internal differences."

Opposition leaders have charged that Iranian officials in Geneva were infuriated by Kazem Rajavi's effectiveness in discrediting a report last February on the human rights situation in Iran by Galindo Pohl, a U.N. investigator.

The slain man's widow, Michelle Rajavi, said she is convinced the mildly worded report by Pohl, a Salvadoran lawyer who visited Iran last winter for the U.N. Human Rights Commission in Geneva, cleared the way for her husband's assassination.

Swiss police said some of the passports of the 13 implicated in the killing were issued in Tehran on the same date and that most of the individuals flew to Switzerland together from Tehran, using consecutively numbered tickets. Several, police said, flew to Vienna right after the shooting.

Rajavi's widow and another brother-in-law, Paris cardiologist Saleh Rajavi, visited the United States this month to denounce what they call Tehran's "terrorist-diplomat" network in Europe, centered in Geneva.

The widow said she fled Switzerland last month because of harassment from unidentified Iranians.

The visiting Rajavis also protested a planned new U.N. human rights evaluation of Iran this summer by Pohl, whose earlier report was called a whitewash by critics in Congress and Europe.

His February report dismissed as "speculation" reports of political prisoners' executions on trumped-up drug charges. Pohl said Iran had held no public executions for five months, despite numerous accounts in government-owned newspapers of public beheadings and hangings.

Dymally's letter pointed out that the State Department's last annual global terrorism report brands Iran "the most active state sponsor" of terrorism in 1989, having backed 28 terrorist incidents and assassinations of "at least five Iranian dissidents" during the year.

Rafi said Iran has "already rejected" the report.

Officials at State, while defending Pohl, agreed this month that his report, based heavily on statements and witnesses supplied by the Tehran regime, was "not an accurate reflection" of Iran's human rights situation, and they expressed hope that the regime would be more "forthcoming" on his next visit.