WASHINGTON — The American military’s mistaken delivery to Taiwan of electrical fuses for an intercontinental ballistic missile raised concerns yesterday over America-China relations and triggered a broad investigation into the security of Pentagon weapons.

While the shipment did not include nuclear materials, the error is particularly sensitive because China vehemently opposes American arms sales to Taiwan. Four of the cone-shaped fuses were shipped to Taiwanese officials in fall 2006 instead of the helicopter batteries they had ordered.

Despite quarterly checks of the inventory, defense officials said they never knew the fuses were gone. Only after months of discussions with Taiwan over the missing batteries did the Pentagon finally realize — late last week — the gravity of what had happened.

Once the error was discovered, the military quickly recovered the four fuses. How it happened, and whether the incident constitutes a violation of any treaty or agreement governing international sales of missile technology, were lingering questions.

At a hastily called news conference yesterday, the no. 2 policy official in Defense Secretary Robert Gates’ office, Ryan Henry, said President Bush as well as Chinese leaders were informed of the mistake — an error Mr. Henry called intolerable.

“I can not emphasize forcefully enough how strong the secretary feels about this matter and how disconcerting it is to him,” Mr. Henry told reporters. He added that in an organization the size of the Defense Department there will be mistakes, but that “they cannot be tolerated in the arena in strategic systems, whether they are nuclear or only associated equipment, as was in this case.”

In a comment directed at the Chinese concerns, Mr. Henry said the error does not suggest that American policies on arms sales to Taiwan have changed.

Taiwan, which split from China amid civil war in 1949, is the most sensitive issue in American-China relations. Chinese officials repeatedly complained about American arms sales to Taiwan during meetings with Mr. Gates in Beijing last fall. America insists it only provides weapons that would allow Taiwan to defend itself.

Beijing claims Taiwan as its own and has threatened to attack should the self-governing island make its de facto independence formal. Washington has hinted that it would go to war to protect Taiwan.

The nearly two-year saga of the fuse shipment began in August 2006. According to the secretary to Air Force, Michael Wynne, the fuses, contained in four large shipping containers, had been sent from F.E. Warren Air Force Base in Wyoming to a Defense Logistics Agency warehouse at Hill Air Force Base in Utah. The containers apparently ended up in an unclassified area, rather than a classified section where they belonged.

In August 2006, the cylindrical containers — measuring nearly 33 inches high and almost 19 inches in diameter — were sent to the government of Taiwan. There they were placed in storage, U.S. officials said.