The service honoured L/Cpl Richard Scanlon, 31, from Rhymney, Caerphilly, and Lt David Boyce, 25, from Bath, Somerset, whose vehicle hit an improvised explosive device (IED).
On Friday night, Governor Jay Inslee was among several hundred people who gathered for an interdenominational prayer service honouring the victims, families and rescuers affected by the mudslide.
President Obama is due to visit Boston on Thursday for a service honouring the victims.
Meanwhile, the Queen attended a service honouring volunteers who served in World War One, 100 years on from the assassination of Archduke Franz Ferdinand in Sarajevo which led to the outbreak of war.
US President Barack Obama has made an impassioned plea for a change in gun control laws, at a memorial service honouring the victims of Monday's shooting at the Washington Navy Yard.
He said the Queen had put aside "selfish goals" and dedicated herself to public service, honouring countless communities and individuals and referred to Prince Philip, saying "our prayers and thoughts are very much with him".
The "private" losses of her lover Ronald, her brother Edward, and her friends Victor and Geoffrey, forced her to question public attitudes towards the war, and an education system that preached duty, service, honour, heroism and glorious death on the battlefield.
Less controversial public service honours go to Jim Barron, head of the independent offices at the Cabinet Office, who heads up the watchdogs that guarantee Whitehall probity, and to a number of local government leaders.
For all the talk of service, honour, compassion and self-sacrifice in Kurt Hahn's teachings, the great educationalist and his disciples seem to have put less weight on the notion that, to learn and grow, children need to be happy.
But it said it was surprised that Mr Cameron had "bypassed" the parliamentary and political service honours committee before taking the decision.
He was recognised internationally for his achievements: in addition to the Nobel, he received the Lasker Award and the Royal and Copley Medal from the Royal Society, honorary doctorates, and distinguished service honours from the Commonwealth of Nations and Japan.
