After five days of intense internal deliberations, Iranian officials met with European envoys here Thursday to seek "clarifications" on a proposed deal that would require Tehran to indefinitely suspend a pivotal aspect of its nuclear energy program that could be converted to military use, Western diplomatic sources here said.

European envoys said they were cautiously hopeful that Iran would agree this weekend to suspend its controversial uranium-enrichment program. But an agreement remained elusive, even though a top Iranian official had suggested earlier that a formal announcement was imminent.

"I am optimistic about a positive answer from Tehran," Iranian nuclear negotiator Hossein Mousavian told Reuters shortly before the ambassadors from Britain, France and Germany were summoned to hear Iran's response.

A European envoy confirmed reports out of Vienna that the Iranian response was "not definitive" but "not disappointing." The clarifications Iran sought were "highly technical," he added.

Details of the proposal have been closely held, but they include commercial and political incentives from Europe, possibly including a light-water reactor that would be more difficult than a heavy-water reactor to convert for use in a weapons program.

Europe has resisted requests from Iran for additional incentives and for flexibility on an early step in the uranium-conversion process, Western diplomats here said.

Europeans diplomats here said they had hoped to have an answer from Iran before British Prime Minister Tony Blair arrived in Washington on Thursday so he could discuss the specifics with President Bush. A deal to get Iran to indefinitely suspend uranium enrichment is only the first phase. The next stage is working out a permanent arrangement to ensure that Iran does not have the capability to produce a nuclear bomb.

Iran is also under pressure to provide an answer in time for the International Atomic Energy Agency to carry out inspections and make a report before its Nov. 25 meeting.

U.S. officials have made it clear they prefer pressing the IAEA, the U.N. nuclear watchdog, to referring the Iranian issue to the Security Council.

The deal was negotiated in Paris talks over the weekend, after which Iranian and European officials said considerable progress had produced a provisional agreement that would be taken back for final approval by Iran's leadership.

The Iranian-European talks have been "anything but easy," German Foreign Minister Joschka Fischer told Germany's parliament Thursday. "Only the full and lasting suspension of enrichment activities . . . by Iran can open the way for results-oriented talks on long-term cooperation," he said.