Leonid Brezhnev is paying his first visit to the West since the Soviet invasion of Afghanistan sent him to diplomatic Siberia in 1979. No matter how many conciliatory gestures he offers in Bonn, they will be shadowed so long as the brutal subjugation of the Afghan people continues. Tens of thousands of demonstrators - against Moscow rather than Washington for a change - have dramatized European concern about Soviet tyranny.
But the long distance Mr. Brezhnev has to go to reach the starting line of peace should not discourage efforts to help him do so.
Thus Chancellor Schmidt deserves credit for inviting the Soviet chief when no other Western leader was ready to receive him in the aftermath of Afghanistan.
Thus also the ''zero option'' proposed by President Reagan on the brink of Brezhnev's journey should not be confused with the ''zero sum'' game in which nobody can win unless somebody else loses.
For the promise of the Bonn talks lies in fortifying a concept of negotiations in which what benefits one benefits all. The sweeping Reagan suggestion for bringing both sides' European nuclear missiles to ''zero'' may be no more likely in the near future than any previous Brezhnev proposal. When the Geneva negotiations on these missiles begin next week, the participants may quickly have to take fallback positions. But somewhere an inch of common ground can be discovered. And then another inch. Neither side losing as much as each side wins in relation to the goal of peace.
To do so, of course, means a determination to do so, a willingness to keep talking. A seriousness at the core whatever the public ploys and counterploys. Mr. Schmidt's stated goal this week is the essential one of convincing Mr. Brezhnev that the Reagan administration is indeed serious about negotiations - something on which the American public itself has had to be convinced after all the hostile rhetoric. It ought to be Mr. Brezhnev's goal to convey serious intentions, too, rather than wasting time on the predicted attempts to seek divisions in Washington-Bonn relations.
Remember that the Americans and the Soviets have negotiated arms agreements before. Their respective economies, though widely disparate, both add new pressures for reducing the drain of enormous unproductive arms expenditures. Both sides also face the rising concern of Europeans who see themselves as the most threatened parties as the arms race escalates. At the same time the mutual interest in East-West trade is growing.
It may be tempting to put all these things on hold until Mr. Brezhnev's land desists from Afghanistan adventuring abroad and repression at home - the latter clouding his trip with a hunger strike by Soviet human rights advocate Andrei Sakharov (who is seeking freedom for his daughter-in-law to leave the country). But Moscow must be given the chance to move in a better direction, as it has sometimes done in the past, without any outsiders' illusions about larger reforms until Soviet society itself evolves.