George Shultz reached a milestone a few days ago - six years as Secretary of State. That makes him the longest-serving member of the president's Cabinet. He not only has longevity, but his final months in office offer the rosiest diplomatic view in many years. Peace seems to be breaking out all over.

For example:- The Russians are pulling their troops out of Afghanistan, giving up their long battle with U.S.-backed rebels in that country.

- The U.S. and the Soviet Union have agreed on a treaty eliminating all medium-range nuclear missiles from Europe and a general thaw has taken place between Washington and the Kremlin.

- The eight-year Iran-Iraq war appears to be on the brink of ending, if not in real peace, at least in a a truce or cease-fire.

- An even longer war in Angola is at the negotiating table, with Cuba, South Africa, and Angola scheduling talks on the withdrawal of all foreign forces from that country.

- Vietnam has agreed to end its occupation of Cambodia and has met with guerrilla factions to discuss withdrawal of Vietnamese troops over the next two years.

Of course, not all of these events are the direct result of American efforts, but the U.S. has had a role in many of them. Shultz is not a speech-maker or a flamboyant personality, but he is quietly effective and is proving that endurance succeeds.

Too often, if a problem isn't resolved in two or three years, the U.S. has a tendency to abandon the issue. Yet long-term persistence is necessary in many cases.

Shultz has had his critics who didn't want the U.S. helping the Afghan rebels, the Angolan rebels, or sending ships to the Persian Gulf. Yet each of those policies appears to have paid dividends.

Not all that has happened is a direct result of U.S. actions alone. The rise of Mikhail Gorbachev in the Soviet Union, and his apparent desire to pull back from points of conflict, plus a more open attitude within Russia itself, has contributed to the optimistic outlook.

However, there remain at least two areas where Shultz has not been able to produce success, despite his best efforts. One is the Arab-Israeli conflict and the terrorism of the Middle East. The second is Nicaragua, where hopes for peace are faltering as the Sandinistas back away from earlier promises of democratic reform. Congress didn't help by halting military aid to the Contras and sending them to the bargaining table essentially empty-handed.

Despite the troubles in Latin America and the Middle East, the world is a more hopeful place than it was when Shultz took the top U.S. diplomatic job in 1982. He doesn't deserve all the credit for what has happened since, but the low-key Shultz has been a major influence.