THE two Asian giants, China and India, may not have reached the landmark agreement which they both claimed yesterday, but they have made two moves which are likely to diminish tension between them. The Agreement on the Maintenance of Peace and Tranquility along the Line of Actual Control in the India-China Border Areas (AMPTLAC), signed in the presence of, but not actually by, the two prime ministers, moves the old enemies closer to a non-aggression pact on the one hand, and towards accepting the line of actual control as the de facto international border. While the full text of AMPTLAC had not been made available at press time, it evidently contains the promise that ''neither side shall use or threaten to use force against the other''. It was the use of force by both sides in the 1962 Border War which instituted a cold war between them. The last major crisis, when another armed clash was widely anticipated, came in 1987-88, when both nations suspected the other of unduly building up force on the contested border. By far the most important sentence in the agreement appears to be that ''pending a boundary settlement, India and China have agreed to respect and observe the line of actual control (LAC)''. Given the near impossibility of any Indian government ending all its claims to the Aksai Chin area in the northernmost parts of Kashmir, it has long seemed that mutual recognition of the LAC was the best possible solution to the Sino-Indian border impasse. Thus, if the LAC is the border, Aksai Chin remains under Chinese control while the northeastern frontier area of Arunachal Pradesh, which China claims, remains under India's. The AMPTLAC carefully stresses that no claims have been surrendered. According to the joint press release, the ''agreement explicitly states that the references to the LAC do not prejudice the respective position of the two countries on the boundary question''. It also promises that so-far inconclusive border negotiations will continue. The agreement promises that the alignment of the LAC will be determined by experts when its course is in dispute. Despite all these caveats the agreement opens the ultimate possibility that the LAC will one day become the de jure as well as the de facto border. However the the limitations of the agreement are clearly indicated when it promises confidence-building measures between the two nations, such as the mutual reduction of forces deployed along the border. It does not precisely stipulate any commitments. Instead the statement says that ''the extent, depth, timing, and nature of reductions will be worked out through mutual consultations''.