"The story is tangled and murky, and it may never be fully unraveled," Mr. Sick writes.

The fate of the hostages was a pivotal issue in the 1980 election. They were taken prisoner when followers of Ayatollah Ruhollah Khomeini, the founder of Iran's revolutionary Government, seized the United States Embassy in Teheran in November 1979. A military operation to rescue them failed in the Iranian desert in April 1980. The Carter Administration hoped that it might obtain their release either through negotiations or a second rescue mission before Election Day, and Reagan campaign officials were concerned that the return of the hostages could swing the election to Mr. Carter. Charges Are Denied

All those involved in the Reagan campaign, including President Bush, have vehemently denied any effort to delay the return, saying they would neither violate the law by operating outside established Government diplomatic channels nor contemplate anything that would have prolonged the captivity of the American hostages.

The issue of back-channel negotiations for the hostages is the subject of a documentary in the "Frontline" series on PBS, to be broadcast on Tuesday night on most public television stations. The "Frontline" documentary, "The Election Held Hostage," deals with much of the same evidence Mr. Sick uses in his opinion piece and includes an interview with him.

Mr. Sick said he has become convinced that there were two meetings between Mr. Casey and Hojatolislam Karrubi in the Ritz Hotel in Madrid in late July 1980. Hojatolislam Karrubi is now the Speaker of the the Iranian Parliament. Mr. Casey died in 1987. The "Frontline" report said he never addressed the allegations.

Mr. Sick's principal source for the Madrid meetings is Jamshid Hashemi, an Iranian arms dealer who said that he and his brother, Cyrus, had helped arrange them. Attending, they said, were Mr. Casey, the Hashemi brothers and an unnamed American intelligence officer. Cyrus Hashemi has since died. Other Sources Named