Reason for encouragement

In a matter of weeks the atmosphere for reducing the nuclear threat to Europe has improved more than most observers would have dared predict. The evolving mood needs to be matched by matters of substance as the US-Soviet talks on theater nuclear weapons get underway next week.

The difficulties are evident. The stated opening positions are far apart.

But an interesting thing has been happening on the way to Geneva. Both Moscow and Washington have been trying so hard to convince the world they are serious about negotiations that they may convince each other. The test will be if their hints of compromise amid the missile numbers game are followed up when the negotiators go to work.

Yes, Mr. Reagan gave Mr. Brezhnev an offer he could refuse. And Mr. Brezhnev in Bonn replied in kind. Yet, courtesy of Mr. Schmidt, dialogue was starting to edge out diatribe. A US administration famous for badgering the Russian bear seemed eager to seize on as much hope as would be consistent without letting down its guard. It found, as we do, ''reason for encouragement'' in the very fact that a dialogue seemed to be emerging. And Mr. Brezhnev, though reportedly still doubting Washington's arms-reduction sincerity, spoke like someone ready to make some adjustments for the sake of seriousness on both sides.

From all accounts the Schmidt-Brezhnev talks were businesslike rather than hectoring or adversarial - a good precedent for the negotiations to come. The two leaders acknowledged differences of opinion, which has to be putting it mildly, but they united on the goal of detente and peaceful, equitable cooperation. It remains a remote goal but one that has seemed more remote in recent years than it does right now.