As a result, officials said, the test is likely to prompt an urgent new effort inside the Bush administration to find ways to counter China’s antisatellite technology.

American officials noted that the US and Russia had not conducted such tests for two decades, and that the international norm had changed, in part because so many private satellites had been launched by many nations. “The Chinese seem out of step on this one, and we don’t know why,” one official said.

But the more immediate mystery about the destruction of the satellite revolves around China’s prolonged silence— and what it says about the commitments President Hu and President Bush have made concerning increasing their communication, and diminishing the secrecy around China’s military buildup.

The timing is significant. Chinese officials have hinted in recent months that they are prepared to grant an American request to establish a military-to-military hot line that may be used to enhance communication. But China has moved slowly to establish the link.

-DAVID E SANGER & JOSEPH KAHN