The U.S. is pressing Vietnam for underwater searches and access to aging witnesses in stepped-up efforts to recover remains of Americans missing from the Vietnam War, Defense Secretary Donald H. Rumsfeld said Monday.

"We still have work to do," Rumsfeld said, though he added that he was pleased Vietnamese military officials had pledged in meetings with him to do more to help recover the remains. "As we all agree, we don't want to forget the importance of this."

Rumsfeld told reporters U.S. officials will work to see if the U.S. can provide technical assistance with underwater recovery efforts.

There are 1,805 American troops unaccounted for from the war, including 1,376 in Vietnam, according to Marine Maj. Jay Rutter, deputy commander of the Joint POW/MIA Accounting Command, which heads the recovery efforts here.

Of those still missing, 453 were lost at sea or over water, according to the Pentagon data.

For Angela Cooke, whose father was missing in Vietnam for 34 years, the MIA recovery work is personal. Just six weeks ago, U.S. military officials in Hanoi notified family members that the remains of Staff Sgt. Calvin Cooke — whose C-130 Hercules cargo plane was shot down over An Loc City in what was then South Vietnam — had been identified.

Later this month, Cooke will finally bury her father at Arlington Cemetery, with full military honors.

"This means a whole lot to all of us — finally being able to say goodbye," Angela Cooke said in a recent phone call from her home in Everett, Wash. And she said the Pentagon's efforts to recover the soldiers' remains in Vietnam must continue. "It's important that they still do this."

Cooke will travel with the remains from the POW/MIA office in Hawaii to Arlington Cemetery, where they will bury her father by her mother's grave.

"It feels so good to finally have closure," Cooke said.

With increased Vietnamese help, more families may get that closure.

According to Rutter, the Vietnamese have agreed to allow U.S. teams to conduct longer searches — for 45 days rather than the previous 33.

U.S. officials are hoping to get access to restricted sites, as well as more archives. He said the U.S. is also hoping to gain broader access to the western highlands, where a large number of losses took place.

"It's getting harder," he said, in part because villagers who were witnesses to many of the crashes during the war are getting older. "The age of the witnesses is a huge issue."

The U.S. also wants greater access to information about MIAs lost in Laos and Cambodia.

Critics of the current Iraq war and Rumsfeld's leadership have likened it to the Vietnam War, noting that in both, public support eroded as time went on with little to show for the loss of American lives.

Despite their bitter history, relations between the U.S. and Vietnam have steadily improved. The U.S. has become Vietnam's top trading partner since the two established diplomatic ties a decade ago, with two-way trade worth $6.4 billion last year.

"I think that it is, it ought not to be surprising, it seems to me, that the United States is developing a very good relationship with Vietnam, just as it ought not to have been surprising that we did so with countries that were engaged on the other side in previous conflicts, whether World War II or Korea," Rumsfeld said.

Rumsfeld, making his first trip to Vietnam as defense secretary, told Vietnamese defense minister Gen. Pham Van Tra that he took a walk around Hanoi and could "feel the energy, the vibrancy of the city."

In another sign of changing times, Rumsfeld stayed only a few blocks away from what was called the Hanoi Hilton, where U.S. prisoners of war, including Sen. John McCain, R-Ariz., were held.