ISTANBUL — SULEYMAN DEMIREL'S return to the prime minister's office here last Thursday - for the seventh time in his long career - is seen as a turning point in Turkey's political life. It marks the end of President Turgut Ozal's personal influence in running the country's affairs.Mr. Demirel's right-of-center True Path Party won last month's parliamentary elections, but failed to gain an absolute majority. So he formed a coalition with Erdal Inonu's Social Democratic Populist Party, a left-of-center group that ran third in the polls. The conservative Motherland Party, founded eight years ago by Mr. Ozal, placed second in the elections, but was left out of Demirel's coalition. Ozal will stay in office until 1996, but he admits the "Ozal era is over." Demirel's return reflects a challenge to the military, which ousted Mr. Demirel in 1980. "Demirel's return to power carries a message for the military," commented the leading daily Milliyet. "The message is that the Turkish people prefer civilian politicians to the military rulers.... Fortunately, the era of such [military] interventions is now over." The coalition of center-right and center-left politicians gives Demirel a wide base - certainly more than if he had joined forces with the ideologically similar Motherland Party. The new government can claim 48 percent of the vote and 57 percent of the seats in parliament. Demirel and Mr. Inonu had no great difficulty in agreeing on a policy program. They prepared and signed a protocol outlining projected economic and political reforms even before agreeing on who would serve in their Cabinet. The package of political reforms would restore the right of students, academics, and labor unions to take part in political activities; grant the state-owned radio and television network autonomy; revise the Anti-Terrorism Act; and reduce the length of time security services are allowed to detain people. Demirel says completing "Turkey's democratization will be [the] government's top priority." Western diplomats welcome these announcements, saying political reform will remove a major obstacle to Turkey's relations with Europe and particularly the European Community, in which Ankara is seeking full membership. "If this promise is carried out, Turkey's image in the West will improve enormously," one diplomat says. The new government says it also wants to improve the plight of the Kurdish population, mainly concentrated in the country's southeastern provinces. The government would go one step further than its predecessor in granting cultural and social rights to the ethnic Kurds, including publication of Kurdish newswpapers. It would enable Kurds in the southeast to administer local affairs. But the government insists that Turkey will remain a "unitary" state, and fight secessionist efforts.