HANOI, Vietnam (AP) _ With an acknowledgment of the bitter past, Secretary of State Warren Christopher arrived today in this former enemy capital to ``build a bridge of cooperation'' in a new era in relations between the United States and Vietnam.

He thus became the first secretary of state to visit Vietnam since the war years of the 1960s and '70s and the first ever to go to Hanoi.

At a government guest in which Ho Chi Minh, the founder of modern Vietnam once lived, Christopher and Foreign Minister Nguyen Minh Cam signed the formal documents in which the two countries agreed to establish relations and exchange ambassadors.

At the end of the ceremony, Christopher announced that Desaix Anderson, a State Department official with long experience in Southeast Asia would be in charge of the U.S. embassy in Hanoi until appointment and confirmation of an ambassador.

Christopher's visit opened with an airport ceremony at which he watched U.S. military personnel receive four wooden boxes containing human remains, possibly of Americans missing from the war.

The boxes were placed in aluminum containers that were then draped with American flags and loaded onto Air Force C-141 jets for a flight to an identification laboratory in Hawaii.

In a brief statement at Hanoi's Noi Bai Airport, Christopher alluded to the dual themes of his trip, saying, ``I am here to lay the basis for a better future, even as we continue to account for the past.''

He expressed thanks for Vietnamese cooperation in locating remains of missing U.S. servicemen and said the fullest possible accounting ``will remain the number one priority on our agenda with the government of Vietnam.''

During his two-day visit, Christopher was meeting with senior officials of the communist government and with U.S. business leaders eager to do business in Vietnam. He also was to officiate at the opening Sunday of the new U.S. Embassy in the Vietnamese capital.

``Closer engagement is in America's interest, first and foremost to achieve the fullest possible accounting, but also because Vietnam is a vibrant country in a region of great importance to the United States,'' Christopher said in his arrival remarks.

``We can build a bridge of cooperation between America and Vietnam.''

His arrival was an extraordinary moment in the troubled history between the two countries.

Immediately after World War II, U.S. involvement in Vietnam was an effort to help France maintain control of its Southeast Asian colony. After the French were defeated and the country was divided between communist North and non-communist South, the United States began a 10-year effort to save the South from being overrun by the North.

The effort cost some 58,000 American lives and killed untold numbers of Vietnamese.

But U.S. firepower and an intensive bombing campaign against the North were not enough. In April 1975, the last Americans were evacuated from Saigon and shortly after the North Vietnamese unified the country.

Christopher's military adviser, Lt. Gen. Daniel Christman, recalled his service in Vietnam from July 1969 to July 1970 as a 101st Airborne Division company commander.

He said that like many others at the time, he counted the days and left with ``a sense of relief.''

This marks Christman's first return to Vietnam. He said he agreed with the decision to establish relations with the former enemy, but he conceded that ``doesn't mean we don't go back with a great deal of memory and some pain.''