Thousands of NATO and Warsaw Pact troops will be on the move beginning this week, according to Western defense officials. Both sets of exercises have been scheduled for some time. NATO officials are concerned - but not surprised - that alliance observers had not been invited to watch the Warsaw Pact exercises even though Soviet-bloc observers will attend the NATO maneuvers.
Under the 1974 Helsinki accords, the two sides are required to notify each other when scheduling military maneuvers involving more than 25,000 troops. They are encouraged to invite each other to the exercises as observers. ''The Warsaw Pact has always been reluctant to invite us even though we always make it a point to invite them,'' an alliance official said.
Notification and the right of observation were among the ''confidence building'' measures adopted in Helsinki a decade ago to help lower the risk of war breaking out in Central Europe by accident or miscalculation.
NATO military experts said they had been told by Warsaw Pact officials that 60,000 air and land troops would be participating in this year's Shield 84 maneuvers in Czechoslovakia, lasting through September. Taking part in NATO's Autumn Forge maneuvers will be more than 330,000 troops, 300 ships, and 2,500 aircraft.
Perhaps the most important of the 26 exercises - certainly the most spectacular - will be the deployment by air and sea of 17,000 troops and 55,000 tons of equipment from the United States to Western Europe beginning on Sept. 6. The US forces will be moved quickly to West Germany, simulating the reinforcement of Western Europe in time of crisis.
NATO military officials call Central Europe, particularly West Germany, the ''core'' of Western defense. But military strategists expressed some concern over what they see as the vulnerability of NATO's northern and southern flanks to Soviet attack.
The Soviet naval forces deployed near northern Norway, for example, outnumber the Danish and West German navies. In eastern Turkey, NATO forces face a ''significant'' Soviet deployment just across the border.
Another strategist said, also regarding the southern region, where alliance solidarity has been compromised by disputes between Greece and Turkey, NATO military experts have begun to worry about increasing Soviet arms shipments to northern Africa and the Middle East.