At a memorial service honoring Britons who died during the Iraq war, the Archbishop of Canterbury said Friday it will take time for historians and moralists to decide if the conflict was justified.

Rowan Williams — an outspoken critic of Britain's role in the war — told a congregation at St. Paul's Cathedral that there are lessons to be learned from it. His audience included Queen Elizabeth II, Prime Minister Gordon Brown, Iraq President Jalal Talabani, former Prime Minister Tony Blair, top officers in the British military, veterans of the war, and families of British soldiers killed there.

"The conflict in Iraq will, for a long time yet, exercise the historians, the moralists, the international experts," Williams said. "In a world as complicated as ours has become, it would be a very rash person who would feel able to say without hesitation, this was absolutely the right or the wrong thing to do, the right or the wrong place to be."

The spiritual leader of the 77 million-member Anglican Communion said, "Perhaps we have learned something, if only that there is a time to keep silence, a time to let go of the satisfyingly overblown language that is so tempting to human beings when war is in the air."

British troops completed their pullout from Iraq in May, ending a six-year campaign that saw 178 British servicemen and women and one civilian Ministry of Defense worker killed.

Prince William — currently training to be a search-and-rescue pilot in the Royal Air Force — attended the service with his father, Prince Charles and his stepmother, Camilla, Duchess of Cornwall. Princess Anne and Prince Edward also were there.

Tracey Hazel, whose son Cpl. Ben Leaning died in Iraq when his vehicle was hit by a roadside bomb in 2007, lit a memorial candle during the service.

"I wanted to be here for Ben and all the fallen — I feel so privileged," she said. "It was so nice they chose one of the parents to do it, as it's them that are left suffering when a loved one dies."

The decision by the Blair administration to join the U.S-led invasion was very unpopular in Britain, and hundreds of thousands of people protested in the run up to the conflict.

In June, Brown announced an inquiry to examine decisions made before, during, and after the operation.

Royal Marine Lance Cpl. Gareth Thomas — who said a prayer during Friday's service — said he was proud of the work that he and his comrades had done in Iraq.

"I like to think we laid the foundations for a better Iraq. Whether that happens or not remains to be seen," Thomas said. "The service was a fitting way, I think, to remember those who did not come back."