TURKEY can fairly claim to be Exhibit A among authoritarian regimes that have been peacefully transformed into competitive democracies. The trouble is, there's no ratchet on politics in Turkey: it keeps slipping back. It slipped back two years ago, when the armed forces swept out a party system that could neither halt an economic rot nor treat a condition of pervasive terror. Some progress on the first front and substantial progress on the second have since been recorded, and as a result the military is giving democracy a chance again.

But it is a very slim chance. In the referendum held Sunday, voters had to take part under threat of going to jail. They approved, by a landslide, a new constitution that makes the current strongman president for seven years, bans the old party politicians for 10, and puts off the formation of new parties and the holding of general elections for a year or more. Turkey in its next stage will be a democracy in not much more than name.

All this might occasion only detached regret if Turkey were not also an American ally and a member of an American-led alliance of free nations. It is properly held to the standards of the company it has chosen to keep. True, there are special circumstances. Ankara adopted martial law two years ago not as the Poles did, to halt a drift toward democracy, but to halt a ferocious Soviet-aided destabilization campaign. It has had to work from the lowest economic base in NATO. Still, Turkey's status remains awkward. No other ally locks up its elected prime ministers and then, even as it asks credit for moving back toward parliamentary rule, bans them from politics.

Meanwhile, American military cooperation with Turkey deepens. The latest development is a plan for the United States to build one new air base and modernize two others in eastern Turkey for, essentially, Persian Gulf purposes. Just what has changed in the 30 years of NATO, or in the three years since the Soviet invasion of Afghanistan, to make these new bases near the Soviet border necessary has yet to be explained publicly.

For the bases, however, the Turks are promised substantial extra military aid. It is said that the administration used this aid to induce the Turkish generals to move back toward democracy. It seems no less apt to say that Turks used the bases to induce Americans to pay less attention to the slowness of their move, and to their continued occupation of nearly half of Cyprus. Congress will have a chance to sort out the issue when the administration goes up to the Hill for the money.