Secretary General Javier Perez de Cuellar, sensing growing support in some quarters in Tehran for the start of a negotiation process that could end the Persian Gulf war, is expected to ask the Security Council today to extend invitations to Iran and Iraq to take part in a new examination of the conflict.

Diplomats whom he has briefed since his return from Baghdad and Tehran last week reported Friday that Perez de Cuellar is convinced that no progress is possible unless the 15-nation council gets more involved in the diplomatic process and changes its previous tilt toward Iraq.

U.N. officials believe an invitation from the council would bolster factions in Tehran that wish to end Iran's diplomatic isolation and begin a dialogue that could bring an end to the 4 1/2-year-old conflict. In fact, diplomats reported, some Iranian officials urged the secretary general to press for the council invitations, as a means of helping them win their internal battle.

The Iranians reportedly told Perez de Cuellar that Ayatollah Ruhollah Khomeini and other members of Iran's power structure remain adamant that Security Council condemnation of Iraqi aggression is an essential condition for any dialogue.

Their hope is that Khomeini and the hard-liners would be satisfied with the opportunity to present their case for such a condemnation before the council, although they cautioned that this is by no means certain.

Iran has boycotted the Security Council since the American hostage crisis, and the council's failure to condemn the Iraqi invasion in 1980 has hardened Tehran's attitude.

On his return, Perez de Cuellar cautioned at a brief press conference Thursday that "there is no breakthrough -- the situation has not changed, in the sense that the two parties are no closer than before."

However, Iranian Ambassador Said Rajaie Khorassani confirmed to reporters Thursday what Perez de Cuellar had been told in Iran -- that the toppling of Iraqi President Saddam Hussein, although still an Iranian objective, is "not a political condition" being demanded by Iran for a cessation of hostilities.

Iran continues to maintain that its other conditions -- the condemnation of Iraq, which would constitute punishment of the aggressor, and a commitment to war reparations from Iraq -- must be met before talks can begin to end the fighting, Khorassani said.

He noted, however, that if Saddam Hussein is condemned and agrees to reparations, "it would be very difficult for him to remain in power."

In his written report to the council, diplomats said, Perez de Cuellar will outline these Iranian stands, which Iraq rejects, and will spell out Iraq's insistence that any discussion of partial measures to mitigate the effects of the war must be linked to talks on a cease-fire.

His conclusion will be that to provide a basis for negotiations, it is essential that the council extend the invitations and that he "trusts" that both combatants will accept them, a diplomat said.

"The scenario as he sees it," said one official who had been briefed on Perez de Cuellar's plan, "is that the invitation is issued -- that should be no problem; that Iran accepts -- that may be the hard part; that the ensuing council debate satisfies Tehran. There is a growing feeling among council members, including the big powers, that they must act in a more balanced way. And then talks can begin on the secretary general's proposals."

Iraq told Perez de Cuellar that Iran was massing troops for a new offensive, and witnesses reported major Iraqi troop movements toward the southern front, Reuter reported from Baghdad.

Iraqi Foreign Minister Tariq Aziz said in a letter that the expected Iranian thrust would be aimed "against Iraq's sovereignty and security."

[In the latest fighting, Iraq said, its forces carried out several attacks on Iranian positions Sunday, killing at least 18 troops, and Iranian artillery pounded two Iraqi border towns, news services reported.]

Perez de Cuellar laid out to both sides an eight-point negotiating agenda, which involved discussions on an end to the conflict and the appointment by each side of negotiators empowered to reach such an agreement. The other points were the exchange of war prisoners, the reopening of closed ports and the banning of chemical weapons, attacks on air and sea transport in the Persian Gulf and air or artillery strikes against civilian population centers.

Iran accepted the proposal as a basis for negotiations -- if its condition on condemnation of Iraq is met -- diplomats reported.

They said Iraq initially rejected the U.N. agenda outright, maintaining that it would enable Iran to prolong the war and would limit Baghdad's military options. But later, Iraq accepted the agenda with three amendments -- all ports and all war prisoners must be included, and there must be a total withdrawal of troops from occupied territories.

The lull in the Persian Gulf fighting that has prevailed since the secretary general's trip was seen by some observers as caused in part by the anticipation from both sides on what Perez de Cuellar might propose. U.N. diplomats pointed out that all other potential intermediaries have fallen by the wayside and that the secretary general remains the only one to have emerged with a mandate to continue mediation efforts.