North Korea, in an apparent softening of policy, accepted a letter Monday from South Korea's national assembly urging it to attend the Seoul Olympics, parliamentary officials said. It was the first communication the communist North has agreed to take from its adversary across the tense Demilitarized Zone since Roh Tae-woo assumed the presidency in February. The letter contained the text of an assembly resolution, passed on July 1, appealing to Pyongyang to abandon its boycott and attend the Games, opening on Sept. 17, to pave the way for eventual reunification of the peninsula. It was not immediately clear whether the North was in fact signaling a change of heart over the Olympics issue.