Beijing has delayed several high-level military exchanges since January, when the Obama administration notified Congress of a plan to sell Taiwan up to $6.4 billion in arms. But the proposed visit by Gates, who leaves for Asia on Wednesday, was the highest-level postponement to date and a sign of continued friction in relations at a time when the Obama administration needs Beijing's help to rein in tensions on the Korean peninsula and to curb Iran's nuclear program.
Gates has spoken out publicly about his hopes to visit Beijing and to put military-to-military cooperation between the United States and China back on track.
He will be in Singapore starting on Thursday to attend a major security conference but Pentagon press secretary Geoff Morrell said a proposed China leg "did not come to be."
A senior US defense official said the Chinese told their American counterparts that it was "not a convenient time" to host Gates but they were not explicit about the reason why.
"It certainly wouldn't be beyond the realm to speculate that this is sort of continued ... reaction to the Taiwan arms sale," the official said on condition of anonymity.
Another US official called it a worrisome "rebuke" given heightened tensions in the region after the United States and South Korea concluded that North Korea was behind the sinking of a South Korean warship in March that killed 46 sailors.
Morrell played down the implications for coordinating Korea policy, saying: "There is not a lack of communication between our respective governments."
China is sending a delegation to the Singapore security conference, but Gates is not scheduled to meet with them.
"China is not sending a very high level delegation to this conference, certainly not an appropriately high level to meet with the secretary," Morrell said.
In Singapore, Gates plans to meet with his South Korean counterpart to convey "our full support for the way in which the Korean government has been handling the crisis" with the North, the senior US defense official said.
"Our commitment to the defense of Korea is and remains unequivocal and that we're committed to continuing to work with Korea and our other allies and partners in the region to try to lessen the threat that North Korea poses to regional stability," the official said.
The Pentagon has expressed frustration with what US officials see as a Chinese "pattern" of curtailing military contacts in response to policy disputes with Washington.
"He (Gates) just doesn't believe that a relationship of this importance can take place in fits and starts. There needs to be a continuous, high-level engagement between these two powers and it can't be derailed by bumps in the road that will inevitably come up," Morrell said.
"We are very much interested in engaging and we think they need to be more interested in engaging," he added.
