PESHAWAR, PAKISTAN -- While professing eagerness to end its devastating occupation, the Soviet Union at the same time is fastening tentacles on every aspect of life in Afghanistan to enhance its post-withdrawal influence.

The involuntary dispatch to Soviet schools of between 15,000 and 25,000 Afghan children, many of them taken from their homes, is a case in point. Why should Moscow do this? ''To make use of them at some future time back in Afghanistan,'' one of the seven mujaheddin leaders based here on the Pakistan-Afghan border told us.

Afghan hatred of the Soviet invader burns hot today. In a country of only 15 million, the war has killed more than 1 million Afghan citizens. It has created 5 million refugees here and in Iran and still another 1 million in Afghanistan.

Yet, despite the extraordinary Afghan military success against its mighty invader, even the smoothest formula for Moscow's withdrawal of its 115,000 troops will leave ominous Soviet influence behind.

For the first time since they kidnapped Greek schoolchildren in World War II, the Soviets have forcibly deported Afghan schoolchildren for indoctrination by Communist apparatchiks back home in the Soviet Union. Although it is not easy to change the political orientation of human beings, and although the Soviet effort to do so has not been an unqualified success, the attempt clearly demonstrates a Soviet intention to maintain future influence.

However rapidly the Kremlin may finally decide to pull out its troops, other roots now deeply planted after nearly a decade of Soviet rule cannot possibly be destroyed fast, if at all. That ensures long-range, continuing Soviet influence, whatever the terms of a political settlement.

The official history books about Afghanistan now being used in most schools are so skewed with political and ideological indoctrination that their record of modern Afghanistan scarcely starts until Soviet troops arrived in 1979. And during these occupation years, the number of schools has dropped by a shocking 80 percent -- through devastation in the war, the decimation of population in villages and towns and the exodus of refugees.

Russian is now the required second language. English is seldom taught. Soviet bureaucrats have reorganized the traditional English educational models into a Moscow model, with all courses flavored with Marxism. It will take decades to erase the Soviet impact on Afghan education.

Another tentacle the Soviets will leave behind is the invisible secret police called KHAD, the KGB look-alike that has been built into a 30,000-man clandestine force. Its agents have penetrated sensitive areas of every government department.

''That is not just defense and internal security,'' Prof. S. B. Majrooh, a refugee from Kabul living here, told us. ''It has deeply rooted itself everywhere, including agriculture'' -- a department that will be critically important in the postwar rehabilitation and reform.

These KHAD agents can hamper reforms, and hampering may become the Soviet game as the Kremlin discourages rehabilitation and reform not made in Moscow and encourages confusion and chaos after it pulls out.

Refugee leaders who regularly make secret visits into their country from here say Soviet tampering with agriculture, coupled with the war itself, has been ruinous, wiping out the livestock essential to the pastoral Afghan economy. When the Soviets withdraw and the population suddenly surges with the return of 5 million refugees, Afghanistan will have to spend scarce hard currency importing food for the first time.

The Reagan administration is jubilant over Soviet withdrawal talk, but the real reason for the withdrawal is the courage and resistance of the mujaheddin, not Washington. The question coming soon is whether the administration will commit itself to postwar rehabilitation and reform with the same zeal it has shown in arming the mujaheddin freedom fighters.

If not, the withdrawal of Soviet forces will be a victory for the United States that is shrouded in heavy troubles ahead.