Jintao and Secretary of Defense Robert Gates are all decidedly worrisome," said Drew Thompson, a China expert at the Nixon Center in Washington.
"Whether Hu Jintao is being snubbed by his own military, or whether he was aware and endorsed the flight test at the time of the Gates visit to signal China's intent to challenge the U.S., both possibilities are equally disturbing for the bilateral relationship."
Gates himself told reporters in Tokyo on Friday he believed the test flight "can be explained by bureaucratic mistakes," adding he had no doubt Hu was in overall control.
"There have been more than a few occasions where the United States military was conducting an exercise or carrying out an activity and not sensitive to the fact that a foreign visitor might be in Washington at the same time," he said.
"But on the whole I think that this is something that is a worry and one of the reasons I have pressed so hard for there to be a deeper, senior level civilian, military dialogue with both civilian and military representatives from both countries is that we have no forum right now on security issues, or military issues, that includes senior civilians and military."
The test flight will draw unwanted extra attention on China's military intentions and muddy the waters ahead of Hu's visit to Washington next week.
Military ties are among the most brittle links between the United States and China, grappling with trade strains, security distrust and human rights disputes that have unsettled relations between the world's biggest economy and the emerging number two.
Chinese government officials and state-run media have repeatedly said the stealth jet should not be seen as a threat. China has repeatedly said its military modernization program is for defensive purposes.
"We shouldn't listen to the words but look at the deeds and its achievements," said Jean Pierre Cabestan, a professor who specializes on Chinese politics at Hong Kong's Baptist University. "One thing the Chinese know pretty well is that there is no soft power without hard power."