WHEN Gary Sick was on President Jimmy Carter's National Security Council, I worked closely with him on the negotiations for the return of our hostages in Tehran from late 1980 to January 1981.
I admire Sick and agree with him that Congress should fully investigate the alleged efforts of the Reagan-Bush campaign team to delay the hostages' release until after the 1980 presidential election.
But on the present evidence, much of it detailed in Sick's recent article (Other Voices, April 17), I am skeptical about whether a deal was made, or, if one was, whether it had any effect on the timing of the hostages' release.
I can readily believe that Cyrus Hashemi -- and perhaps other Iranian middlemen -- made an effort to negotiate some type of deal with the Republicans.
I know the late Hashemi tried to serve as an intermediary for the Carter White House because, at the request of his lawyer, several of us met with him in New York in the fall of 1980.
Hashemi claimed a family relationship with Hojatolislam Hashemi Rafsanjani, then speaker of the Iranian parliament and now president of Iran.
He offered to open a new negotiating channel to the Iranian government. We encouraged him to do so, but nothing came of it.
A few weeks later U.S. Customs and Justice Department officials notified us of evidence that Cyrus Hashemi, along with his brothers Jamshid and Reza, were involved in illegal arms exports to Iran via Kennedy Airport; when confronted, they had said they had our permission.
We denied any such blessing and told the investigators to proceed.
It is plausible that the Hashemis also were in contact with Republicans, as Jamshid now claims.
It is even plausible that William Casey and others on the Reagan-Bush team may have been tempted into a meeting or two, although Casey, ever the spy buff, would doubtless have appreciated the risks of exposure.
But what I cannot get around is the undeniable fact that after President Reagan took office, his own law enforcement people went on to prosecute the case against the Hashemis that the Carter administration had started.
In July 1984 they indicted the Hashemi brothers. Jamshid and Cyrus Hashemi fled the country; their younger brother Reza pleaded guilty.
All this hardly could have happened if the Hashemis had actually made a pre-election deal with the Reagan campaign team or had serious negotiations with Casey or any other visible member of the team.
If they had, then in 1984 the Hashemis would have held the royal flush of all blackmail hands, and had the Reagan team done what has been alleged, the Hashemis' prosecution would certainly have been dropped to buy their silence.
In fact, the Hashemis' bargaining position was so weak that the prosecutors pressed Cyrus into cooperating with an elaborate Customs Service "sting" that resulted in the 1986 indictment of another arms-smuggling ring -- one that turned out, to the prosecutors' surprise, to include several middlemen in the Iran-contra scandal.
The Reagan administration later dropped this indictment, ostensibly because Cyrus Hashemi, a key prosecution witness, died in 1986, before the trial.
"October Surprise" theorists have raised, however, an intriguing question: Why did President Carter's hostage negotiations, which had taken a very auspicious turn in August 1980, suddenly turn cool after the November election?
I do not know, but there are several good hypotheses other than a deal with the Republicans.
* On Sept. 22 Iraq launched its surprise attack on Iran and achieved a deep initial penetration into Iranian territory.
The Iranians did not manage to stabilize the front until the American election. Until then, they were much too preoccupied with repelling the invasion to conduct serious negotiations with us.
* Rafsanjani and his Islamic Republican Party did not consolidate their internal power until the fall of 1980.
Until they had done so, a deal with the Carter administration would have exposed them to domestic attack from the far-right mullahs and from Abol Hassan Bani-Sadr, the quixotic president who was battling them for power and who strenuously opposed the deal the Carter administration concluded in January 1981, calling it excessively favorable to the United States.
* Two days before our presidential election, the Iranians resumed negotiations with the lame-duck Carter administration.
To move the negotiations along we warned the Iranians that if they waited for the Reagan administration, it might insist on the unconditional return of the hostages without any American commitment to unfreeze the billions of Iranian bank deposits we had frozen.
If the Reagan campaign team had secretly offered more generous terms to the Iranians in exchange for delaying release of the hostages, it is hard to see why they would make a deal on less generous terms with us just before Reagan took office.
There is another puzzlement: After the Iraqis invaded, the