THE 10 T-72 battle tanks that stood in front of the Russian Republic's parliament building to defend it from attack by fellow units of the Red Army were visible proof of the split in the Soviet Armed Forces exacerbated by the attempted coup.From the first hours of the coup, there was evidence that the putsch plotters did not command the allegiance of a large portion of the 3.8 million-man Army. A very small number of units were actually involved in the coup actions, which were confined to Moscow, Leningrad, and the three Baltic republics. This suggests that the junta could not control broader forces. Moreover, the units that joined the coup - such as the Tamanskaya Motor Rifle Division and the Paratroop Division from Ryazan which were deployed in Moscow - were elite, virtually all-professional forces. The former is a showpiece unit, turned out for visiting foreign military officials. They were backed by the Interior Ministry's own elite, "black beret" special forces. The conscript-formed motorized infantry divisions that are the mainstay of the Soviet Army remained in their barracks. And according to Pentagon intelligence reports, there was an eerie absence of activity within those forces. They were not placed on alert, nor was there evidence of the heightened communications between Defense Ministry headquarters and the military district commands that many experts expected to see in such a military-backed coup. There were also hints that a significant portion of the Soviet Armed Forces General Staff were, at most, passive bystanders to the coup. The only military figure publicly with the coup was Defense Minister Dmitri Yazov. It has been presumed, given his position and known political views, that Lt. Gen. Boris Gromov was also a participant. General Gromov is an Afghan War hero who was appointed Deputy Interior Minister late last year, a move widely seen as an attempt to tie the military more closely to enfor cing political order within the country. But the man who, most interestingly, has been absent during these past days was Chief of the General Staff Mikhail Moiseyev, who has emerged after the coup as the acting Minister of Defense. That fact would not surprise some Soviet observers, because General Moiseyev had signaled he was at odds with General Yazov and Deputy Defense Minister Valentin Varennikov, both considered extreme conservatives. Moiseyev's break with them was most evident in July, when he helped to negotiate a conclusion to the START treaty limiting nuclear arms, and to resolve differences over implementing the treaty to limit conventional forces in Europe. Both treaties were targets of conservatives, who saw them as unequal and part of the retreat of Soviet power under Mikhail Gorbachev. A well-informed Soviet military expert closely tied to reform circles gave further evidence of a deep split developing in the military. In a July interview, he revealed that a group of senior military officers at the level of deputy commanders of military districts had secretly joined to promote a serious new effort at military reform. The official version of military reform backed by Yazov and others was already widely discredited as a largely paper affair. These officers, the source said, were convince d of the need for serious cuts in defense spending, for conversion of the defense industry to civilian production, and for a new security relationship with the West. According to the expert, the group sought Mr. Gorbachev's support to organize a study team to draft a new reform plan. Gorbachev urged the group to move quickly, far more rapidly than they had planned, to complete their work. He told them, the source said, to get the work done by August. Did Gorbachev know something even then about the dangers awaiting them? There is no clear evidence of that, but he was at least aware, at that point, that the military was divided at the highest level on basic policy issues. That split may ultimately be what saved Gorbachev's life and his government.