Commerce Secretary Malcolm Baldrige said his talks with Chinese leaders had begun in an excellent atmosphere. He said the purpose of his five-day visit was to restore the momentum that previously marked US-China ties. One of the sore points between the two countries is US arms sales to Taiwan. But Mr. Baldrige said he did not expect the issue to dominate trade issues. He gave no details of the thorniest trade problem - US reluctance to sell to China certain computers and other items with potential military applications.