On a sparkling day, trucks stretched northward from Panmunjom as far as one could see along a winding road. Music, mostly intended to be stirring, blared from loudspeakers somewhere in northern territory. Officials from both Koreas, guards, military observers, Communist-bloc diplomats - in all, people from 14 countries - gathered by the dozens along the imaginary demarcation line.

The mood, far from buoyant, was nonetheless genial. Usually hard-eyed border soldiers from the two Koreas softened slightly and chatted. Chinese Army officers on the northern side took turns taking one another's picture. Soviet journalists sought out Americans to ask questions.

But, in the end, bureaucracy and briskness tended to dominate. Customs Checks Carried Out

Red Cross officials from the North had been asked to give their southern counterparts the names and photographs of each of the 800 drivers and other relief-supply workers who would cross the border. Customs inspectors in blue uniforms, carrying albums of pictures and names, checked each truck as it came through. Like other visitors to South Korea, the North Koreans could not enter or leave without going through customs and immigration checks.

A second delivery of supplies is scheduled to be made here on Sunday, along with shipments of 100,000 tons of cement to two South Korean ports, Inchon and Pukpyong. Four North Korean ships entered coastal waters off Inchon this afternoon, but a fifth ship loaded with cement had run aground, South Korean officials reported.

In addition to the cement, North Korea is scheduled altogether to turn over 7,200 tons of rice, 550,000 yards of cloth and 759 cases of medicine. The South has said that, after a quarantine period for the food, the material would be distributed to flood victims - even though the Government said earlier that everyone in need had already been assisted.