In an apparent concession to China on the eve of a Sino-Soviet summit in May, Moscow said it will withdraw three-quarters of its troops from Mongolia. Foreign Ministry spokesman Gennady I. Gerasimov said the cut is in addition to an announcement by Mongolia this week that it will reduce its armed forces by 13,000 soldiers and trim its military budget by 11%. Gerasimov did not say how many Soviet soldiers are in Mongolia, but Western estimates put the total at about 50,000. Western experts see the move as a gesture to China, which has long urged the withdrawal of all Soviet forces from Mongolia. The Kremlin in December announced the plan for a troop cut but gave no figures.