Iran today rejected a request from President Clinton for help in arresting those behind the 1996 bombing of an apartment building housing U.S. troops in Khobar, Saudi Arabia, in which 19 American servicemen were killed.

"These events have nothing to do with Iran," said Foreign Ministry spokesman Hamid Reza Asefi. He qualified as "unfounded allegations" information cited by U.S. officials suggesting some suspects may have traveled to Iran after the bombing and that Iranian officials may have been involved.

Clinton sent a message in August to Iranian President Mohammed Khatemi seeking cooperation in U.S. efforts to investigate the bombing and bring those responsible to justice. The exact nature of Iran's formal response remains unknown.

Reports widely circulated here say Clinton's letter, or documents accompanying it, also sought specific help in taking custody of two Arab suspects living in Iran. But State Department spokesman James P. Rubin has denied these reports, saying Tuesday that the letter made no "specific requests" beyond the appeal for cooperation.

Foreign Minister Kemal Kharrazi, in a meeting with reporters last Friday in New York, denied any Khobar suspects are living in Iran. "That has been an internal issue for Saudi Arabia," he added when asked about Iranian willingness to help. "We had nothing to do with it."

Although most Iranian officials viewed Clinton's letter as friendly in tone, several have taken exception to what they called a veiled threat at the end of the document. According to Iranian sources, Clinton told Khatemi he could face tremendous domestic pressure to take action--presumably meaning retaliation against Iran--unless the issue of Iran's possible connection to the bombing is solved.

Since Khatemi was elected in May 1997, Iran and the United States have moved toward improving ties with cultural exchanges, symbolic gestures and toned-down rhetoric on both sides. Still, both countries are waiting for concrete improvement, and the reports of Iranian involvement in the Khobar bombing have made this even more difficult.

Rubin suggested Tuesday that Iranian cooperation in the Khobar investigation would be "a first and significant step" to improved relations and an end to economic sanctions. But Reza Asefi called Rubin's comments "blackmail."

"The tone of the United States has changed, but in practice we have not witnessed concrete acts," Mohammed Ali Abtahi, Khatemi's chief of staff, said in an interview today. Ali Abtahi said Iran and the United States have "a long and complex history, which cannot be improved without some difficulty."

Correspondent Nora Boustany contributed to this report from New York.