ANKARA, TURKEY -- Turkey shows signs of experiencing an identity crisis as changes abroad and at home challenge the westward-looking, secular principles on which the modern republic was built early in this century, according to diplomats and other analysts.

In recent months, Turkey's key relationships with the West have been changed, raising new questions about the country's national identity, which already has faced challenges from Moslem fundamentalists.

For centuries, Turkey was the core of the Ottoman Empire and the political center of the Moslem world, whose sultans ruled neighboring lands with military might and the religious authority of the Moslem caliphs. In World War I, the Ottomans' disastrous alliance with Germany brought the final collapse of the declining empire and allowed the rise of a determined nationalist, Mustafa Kemal Ataturk, who turned his country resolutely westward.

In the decades since, Turkish leaders have maintained the alignment, joining the North Atlantic Treaty Organization and anchoring the alliance's southern flank, and applying for membership in the European Community.

But, with the decline of NATO's Cold War confrontation with the Soviet Union, Turkish politicians have expressed fears in the press here that their nation's importance to its allies may be declining.

Officials also worry that East-West disarmament may compromise Turkey's hopes of modernizing its aging weaponry with F-16 aircraft and new tanks. Visiting U.S. officials have told Ankara that a reduced U.S. global role eventually will bring cuts in military aid to Turkey, which is set for $545 million in fiscal 1991.

NATO's transformation into a more politically oriented organization and the possible decline of its integrated structure raise fears that Turkey may no longer be able to take Western support for granted in dealing with its unstable neighbors: Christian Armenians in the Soviet Union, Islamic fundamentalist in Iran and hostile governments in Arab Iraq and Syria.

The 12-nation European Community last December indefinitely postponed a decision on Turkey's application for full membership, and Turkish officials have expressed worries that the setback may prove permanent. The EC cited Turkey's near 3 percent annual population growth, human rights violations and a comparatively underdeveloped economy in rejecting Turkey's application.

But Turkish officials suspect that Western Europe really objected to absorbing 55 million Moslems into what amounts to a Christian club and say they fear the EC will give priority to integrating Moscow's former East European satellites.

Such shocks to basic tenets of Turkish policy, many diplomats and local commentators say, come as Turkey appears to be drifting dangerously, with the prospect of a weak coalition government on the horizon. The ruling Motherland Party scores in the low teens in opinion polls. Its leader, President Turgut Ozal, is scarcely more popular.

After years of growth, Turkey's experiment with an export-driven market economy is beset by problems such as 70 percent inflation and feather-bedded state enterprises.

A civil war rages in the southeast, where Kurdish rebels are fighting for self-determination -- a demand that directly opposes Ataturk's legacy of an all-powerful centralized government reluctant to grant cultural rights or autonomy to minorities.

Analysts say the army, in particular, worries that granting Kurdish cultural demands will lead to the country's dismemberment, which Ataturk overcame by thwarting Greek, French and British designs on Turkey after World War I.

The turmoil in neighboring Soviet Armenia has heightened fears of minority claims. So, too, has American attention to the Armenians' claim that Turkey killed as many as 1.5 million of its Armenian minority population during and after World War I.

Turkish officials showed their sensitivity to the issue last winter, imposing curbs on U.S. military activities here when the U.S. Senate considered a resolution supporting the Armenians' position. Turkish officials fear such support, which included a statement by President Bush in April, could lead Armenians to claim reparations or even revisions of Turkey's eastern border.

Also, Moslem fundamentalism is on the rise here, making its influence felt in the Education and Culture ministries and reportedly also in some counterintelligence and police operations.

Even the army, Ataturk's vanguard for a lay society, has not proved immune. Recently, 150 noncommissioned officers suspected of fundamentalist leanings were forced out of the armed forces.

Although secular Turks insist the threat is more serious than a decade ago, when Iran's revolution was at its most influential, some specialists are not convinced and cite the traditional antagonism between the mainstream Sunni Islam of Turkey and the Shiite Islam of Iran.

Nonetheless, pro-Iranian fundamentalists were widely thought to be responsible for the recent murders of a prominent constitutional law specialist and the editor of a major daily newspaper.