Then-Secretary of State Hillary Rodham Clinton meets with Vietnamese Communist Party Secretary General Nguyen Phu Trong under a bust of the founder of modern Vietnam, Ho Chi Minh, in Hanoi on July 10, 2012. (BRENDAN SMIALOWSKI/AFP/GettyImages)

President Obama on Tuesday will meet with the general secretary of Vietnam's Communist Party, the first such visit at the White House since the two countries normalized relations two decades ago.

Obama and Nguyen Phu Trong are expected to discuss a range of issues, including the 12-nation Trans-Pacific Partnership (TPP) trade accord, bilateral defense cooperation and human rights, the White House said in a statement.

The meeting will mark a rare time that Obama has played host in the Oval Office to a foreign leader who is not the official head of state. Obama met with Vietnamese President Truong Tan Sang at the White House in 2013, and he met with Prime Minister Nguyen Tan Dung during a regional summit in Burma last fall.

Administration officials said the meeting will provide a chance for Obama to engage directly with Trong, who is perhaps Vietnam's most powerful figure even though he does not have an official government position. Vietnam is among the nations negotiating the TPP trade pact with the United States, and over the past two years, Vietnam has been alarmed by China's maritime operations in the South China Sea.

U.S. officials see an opportunity to improve relations with Vietnam.

"We see the visit as an opportunity to continue to build on that positive momentum," a State Department official said this week during a background briefing for reporters. "Specifically, it's important for head of the party [to visit]. The party is the only party in Vietnam. It's hugely important in all decision-making, and it tends to be a more conservative element of Vietnamese leadership."

Human rights advocates have expressed alarm at Trong's visit, saying that nation has not made significant progress in releasing political prisoners and improving labor rights for workers.

There has been speculation among some foreign affairs experts in Washington that Obama could make his first visit to Vietnam this fall during his trip to Asia, but the White House has not confirmed such a visit.