CLINTON'S SERVICE PLAN THREATENED.(MAIN)

Byline: Associated Press

Senate leaders sought a compromise on President Clinton's national service plan Tuesday in the face of a potential filibuster by Republicans complaining about its cost.

A vote to cut off debate on the proposal was canceled and Democrats admitted they lacked the 60 votes needed to adopt the bill over GOP objections.

"Discussions are under way in an effort to reach agreement and permit passage of the bill," said Majority Leader George Mitchell, D-Maine. He said the cloture vote would be rescheduled if no agreement could be reached.

Sen. Nancy Kassebaum of Kansas, ranking Republican on the Labor and Human …