China deserved praise for its efforts in securing the recent six-nation deal on North Korea's nuclear programme, Christensen said.
But, he said, Beijing needed to take a stronger stand on a range of the other international issues that affected US interests.
Christensen also noted China's considerable influence in Sudan and said the US expected Beijing to use the leverage gained from its imports of Sudanese oil to persuade Khartoum to accept a UN peacekeeping force in Darfur.
China, "with some justification, is seen as Khartoum's patron and benefactor", he said.
Christensen's comments are the latest words of concern from the Bush administration over China's growing influence on the world stage.
Last month Dick Cheney expressed worries over Beijing's military build-up, saying China's recent anti-satellite weapon test raised the prospect of an arms race in space.
Cheney's comments echoed earlier remarks from Condoleeza Rice, the US secretary of state, who said China's military activities were "outsized for China's regional and even global interests".
In his testimony on Tuesday Christensen also raised concerns over China's growing military arsenal facing Taiwan, "as well as Beijing's refusal to renounce the use of force against Taiwan".
"We believe these circumstances constitute important factors for instability in cross-Strait relations," he added.
US officials say China has hundreds of short-range ballistic missiles aimed at Taiwan.
China and Taiwan split amid civil war in 1949.
Since then, the Communist mainland has repeatedly threatened to attack if Taiwan makes its de facto independence permanent.
Washington has no formal diplomatic ties with Taiwan but maintains extensive unofficial relations and has pledged to see that Taiwan has the means to defend itself.