JERUSALEM, Aug 11 (Reuters) - Israeli troops were not ready for the violent resistance they met when they boarded a Gaza-bound aid ship and ended up killing nine pro-Palestinian activists, the country's top military officer said on Wednesday.

Speaking to an inquiry, Israeli Defence Forces Chief of Staff General Gabi Ashkenazi gave the most detailed explanation so far of what went wrong with the military plan in the May 31 raid, which sparked a world outcry.

IDF commandos failed to clear the decks with stun grenades, and rappelled from their helicopter straight into a brawl with men wielding iron bars and knives, Ashkenazi said.

The raid quickly became "chaotic", he said. "After the first soldier went down the rope there was no choice but to continue with the plan."

International condemnation of the raid persuaded Israel to ease restrictions of its Gaza blockade, which is aimed at preventing arms reaching the territory but also aggravates the privations of 1.5 million mostly aid-dependant Palestinians.

The nine activists who were killed were all Turks, and the raid almost ruptured Israel's relations with once-close Muslim ally Turkey.

The raid was seen at home as a debacle for Israel in terms of public relations and international image, although many Israelis consider the interception justified in principle.

Ashkenazi was the third senior figure to address the inquiry this week after Prime Minister Benjamin Netanyahu and Defence Minister Ehud Barak appeared before it.

The commission offers a closely-managed forum in which Israeli leaders can argue their case, separate from an independent investigation into the "flotilla affair" which opened at the United Nations in New York on Tuesday.

CLEAR THE DECKS

The operation to stop the ship reaching the Israeli-blockaded Gaza strip depended for its success on getting as many commandos on deck as possible in the shortest time, Ashkenazi said. But that did not happen.

Accurate suppressing fire from alongside the ship would have cleared the deck of anyone ready to violently resist the boarding, he said. This was "a lesson we have learned". Israeli leaders insist Israel was legally within its rights to stop a deliberately provocative bid to break its naval blockade of the Gaza Strip, put in place to stop heavy weapons reaching the Hamas Islamist militants who control the enclave.

The investigating panel has so far has heard mostly pre-scripted statements. Cameras are turned off and reporters excluded for a closed-door question session. It is not the sort of public grilling familiar to viewers of televised U.S. Congressional hearings.

Israeli media have treated the inquiry with scepticism, focussing predominantly on what they see as buck-passing and finger-pointing in the top ranks of the leadership.

Netanyahu, Barak and Ashkenazi conceded that intelligence was imperfect. As Ashkenazi put it "we didn't know enough" about the Turkish activist group whose members were ready for a fight on deck and ended up in a lethal battle with its commandos.