WASHINGTON — The nation’s top intelligence official said Thursday a one-paragraph assessment about North Korea’s ability to arm a nuclear missile was mistakenly declassified by the Pentagon’s intelligence agency, an inadvertent disclosure that revealed competing views on the country within U.S. spy agencies.

After the conclusion became public at a congressional hearing last week, the official, James Clapper Jr., director of national intelligence, issued a statement saying the position by the Defense Intelligence Agency (DIA) did not reflect the consensus view of the 15 other intelligence agencies.

But Clapper, in testimony to the Senate Armed Services Committee on Thursday, offered a fuller explanation of why the DIA’s conclusion last month — with “moderate confidence” — that North Korea has learned how to shrink a nuclear weapon to fit into a nuclear warhead was at odds with all the other intelligence agencies.

“The difference has to do with the confidence level in the actual ability of the North Koreans to make a weapon that will work in a missile,” Clapper, said, adding that since the North has yet to test such a weapon, “neither we nor the North Koreans know whether they have such capability.”

Clapper continued: “DIA has a higher confidence level than the rest of the community on that capability. That’s the difference.”

At issue is a seven-page classified report, one sentence of which was mistakenly labeled unclassified, Clapper said.

The assessment’s existence was made public April 11 by Rep. Doug Lamborn, R-Colo., in a budget hearing of the House Armed Services Committee.

Hours after the disclosure, Clapper issued a statement playing down the assessment of the DIA, saying “North Korea has not yet demonstrated the full range of capabilities necessary for a nuclear armed missile.”

President Obama said in an interview broadcast Tuesday that he did not believe North Korea had the ability to make a nuclear weapon small enough to fit atop a missile.

North Korea has conducted three nuclear tests, including one this year. and in December shot a ballistic missile as far as the Philippines.