Turkish generals are to take over command of land and air forces defending NATO's southeast flank, from American officers, it was announced today.

The command restructure, made public simultaneously in Ankara and at NATO headquarters at Casteau, Belgium, will take place in mid-1978.

Turkish Foreign Minister Ihsan Sabri Caglayngil said the switch was a "natural necessity" following Greece's withdrawal from NATO's integrated military command in 1974, which left Americans in charge of exclusively Turkish units.

The NATO regional commands affected are Headquarters Allied Land Forces for Southeastern Europe, currently commanded by U.S. Gen. Sam Walker, and the Sixth Allied Tactical Air Forces Command, whose commander is U.S. Lt. Gen. Benjamin Bellis. Both are located in Izmir, on Turkey's Aegean coast.

A forward headquarters under Walker's command, now located in Thessaloniki, in northen Greece, would be shut down as a result of the changes. In addition, the two formations would no longer be charged with the defense of Greek Macedonia.

The end of the integrated defense command for the southeastern flank, which reflected political tensions between Greece and Turkey since 1974, has disturbed some senior U.S. officials in NATO.

Gen. Alexander Haig, the NATO commander, said the changes were necessary since Greece had removed ots formations from the integrated command following the Turkish invasion of Cyrus in 1974.

Haig said he believed the change would facilitate Greece's return to NATO's integrated military structure and hinted that if Greece wanted it, a separate command dealing with Greek forces could also be established.

A high-ranking Turkish official in Ankara said, however, that the Turks would not accept Greece back into the integrated military command as long as the Greece's supporters in the United States continued to agitate for prolongation of the congressional arms ban against the Turks.

Until 1974, the integrated command at Izmir included four field armies: three Turkish, with a strength of about 400,000, and one Greek, with nearly 150,000 men, and the Air Forces of both Turkey and Greece. Each American commander had Turkish and Greek deputies and Turkish and Greek officers were assigned the Izmir headquarters staff.

Following the Turkish invasion of Cyprus, however, Greece withdrew its forces and headquarter's personnel from the Izmir commands, charging NATO had done nothing to stop the Turkish operation.

The Alliance's southeastern defences were further weakened by the imposition by Congress of an arms embargo against Turkey and severance of U.S. military aid, resumption of which U.S. legislators have made conditional on Turkish withdrawal from Cyprus.