Prime Minister Margaret Thatcher left Monday for a two-day trip to Frankfurt where she is expected to sound out Chancellor Helmut Kohl about his reservations on modernizing NATO's short-range nuclear missiles based in West Germany.

Thatcher's trip to West German follows a visit to 14 NATO nations last week by Secretary of State James Baker, who said he expected the issue of modernizing short-range nuclear missiles in Europe to be resolved within the next three months prior to a summit of NATO leaders tentatively scheduled for the last half of May.Earlier this month, Kohl, with backing of Foreign Minister Hans-Dietrich Genscher, said he saw no need to modernize the West German-based lance missiles, which have a range of about 75 miles, until 1991 or 1992 - after the next German election.