BEIRUT, Lebanon (AP) _ U.S. Marine Lt. Col. William R. Higgins was planning a mission to rescue American hostages in Beirut before he was abducted by pro-Iranian forces, a PLO official was quoted as saying today.

The rescue plan was disclosed in a transcript of Higgins' interrogation by his captors, Bassam Abu Sharif, a Palestine Liberation Organization spokesman, was quoted as saying in the Beirut daily Ad-Diyar.

''We have seen a transcript of the interrogation of Higgins,'' he was quoted as saying.

Higgins, 43, of Danville, Ky., was chief of a 76-member observer group attached to the U.N. Interim Force in Lebanon when he was kidnapped near the southern port city of Tyre on Feb. 17.

A pro-Iranian Shiite Moslem group calling itself the Organization of the Oppressed on Earth claimed responsibility for Higgins' abduction, charging he was a CIA spy.

The United States and the U.N organization have denied the charge.

''We know from seeing the transcript of the interrogation of Higgins ... that he was preparing a large-scale operation under the slogan of rescuing all the American hostages (in Lebanon),'' Abu Sharif was quoted as saying in the newspaper, which is based in Christian east Beirut.

Abu Sharif did not say how the PLO obtained the purported transcript.

He also was quoted as saying that Higgins ''had headed the operations department of the U.S. Delta Force and had arrived in Lebanon wearing (the U.N.'s) Blue Beret.''

The Delta Force is better known as the Rapid Deployment Force, a U.S. group set up to act against terrorism and other threats to American interests.

He also said the ousting from Beirut of guerrillas loyal to PLO Chairman Yasser Arafat's was part of a ''Syrian-American plan.''

Arafat's loyalists Friday left the refugee camp of Bourj el-Barajneh, their last stronghold in Beirut, after it fell to Syrian-backed PLO dissidents of Col. Saeed Mousa's Fatah-Uprising faction.

Eighteen foreign hostages are believed held in Lebanon, including nine Americans. The longest held is 40-year-old Terry A. Anderson of Lorain, Ohio.

Anderson, the chief Middle East correspondent for The Associated Press, was kidnapped March 16, 1985.

Most of the hostages are believed held by factions loyal to Hezbollah, or Party of God, a pro-Iranian Shiite group.