President Clinton met yesterday with a top North Korean military commander, the first encounter between a U.S. president and a senior official of the hard-line communist nation.

Jo Myong Rok, vice chairman of North Korea's powerful National Defense Commission, bore a letter from North Korean leader Kim Jong Il that contained ideas on building a better relationship with the United States, the White House said.

Jo's three-day visit, which began Monday in San Francisco, has fed cautious optimism among U.S. officials that North Korea is beginning to emerge from half a century of isolation and Stalinist dogma.

The United States had expected North Korea to send a Foreign Ministry official. Kim's decision to send Jo "conveys a very important message to us and the citizens of North Korea . . . that this effort to improve relations is one shared not only by the civilian side, the Foreign Ministry, but by the military as well," said Wendy R. Sherman, a special adviser to Clinton on Korean affairs.

"Their relationship with us is beginning to move," said Donald P. Gregg, a former U.S. envoy to South Korea who is chairman of the Korea Society, a nonprofit group.

Jo, 70, a fighter pilot in the Korean War, was a friend and adviser to Kim's father, Kim Il Sung, North Korea's reclusive founder and longtime dictator. He is a key commander of North Korea's military, which Gregg described as "the only well-fed institution in North Korea" since the collapse of the Soviet Union deprived the country of the main prop for its stagnant economy and led to widespread hunger.

With hundreds of thousands of troops stationed along the demilitarized zone with South Korea, the North Korean army remains a potential adversary of the United States, which has 38,000 troops on southern side of the divided peninsula.

"If we're going to move toward genuine improvement in our relations, we're going to have to establish some kind of relationship with the North Korea military," Gregg said. "The only one we've had up to now is one of bristling hostility."

Sherman described Jo's meeting with Clinton as "very positive, direct and warm," although she said it was an introductory encounter and did not yield any agreements.

During the 45-minute session in the Oval Office, she said, Clinton summarized America's main concerns about North Korea, including its nuclear and ballistic missile programs, its alleged support for terrorism, its arms sales and the U.S. desire to recover the remains of American soldiers who died in the 1950-53 Korean War.

Jo's reception was unusually warm for a representative of a country that does not have diplomatic relations with the United States. He also spoke yesterday with Secretary of State Madeleine K. Albright and is scheduled to meet today with Defense Secretary William S. Cohen.

One of North Korea's principal goals appears to be its removal from the State Department's list of countries that sponsor international terrorism, which could clear the way for lifting sanctions on trade. On Friday, the United States and North Korea issued a statement pledging to exchange information about terrorist threats. The United States still wants North Korea to expel Japanese Red Army members who hijacked a Japanese airliner in 1970.

U.S. officials also hoped that Jo would clarify whether North Korea was serious about a proposal to give up its missile development effort in exchange for international help in launching civilian satellites.