A day after the Turkish armed forces overthrew the democratically elected government of Prime Minister Suleyman Demirel, life throughout the country here appeared today to be returning to a relative, if uncertain, normality.

Although there were still few reports from the provinces where extremists of the left and right had established virtual autonomous fiefdoms in recent months, all of the major urban centers were reported calm with businesses reopening and people, hesitatntly, returning to the streets from which they had been barred by all-day curfews yesterday.

In Istanbul and in the Turkish capital of Ankara, the Army tanks that had manned strategic squares and intersections rumbled back to their barracks, leaving only the marginally less menancing armored personnel carriers in place to back up the Army roadblocks.Troops there were selectively stopping traffic for identification checks and car searches throughout the cities.

Demirel and opposition leader Bulent Ecevit, who were among the nearly 100 politicians and parliamentarians put under "protective custody" by the military, were moved with their wives to a military camp in Gallpoli, on the Dardanelles Strait.

The military-junta also confirmed that Necmettin Erbakan, the head of the Moslem fundamentalist National Salvation Party, whose advocacy of an Islamic republic particularly enraged the military command, was similarly interned at a naval base on the Aegean Island of Usunada off the coast of Izmir.

Military authorities, meanwhile, issued an ultimatum to retired colonel Alparslan Turkes, the leader of the neofascist National Action Party, the sole major politician who escaped detention. Although the military would neither confirm nor deny it, one newspaper alleged that Turkes was warned of the impending coup by sympathizers in the Army who helped him flee his home an hour before the military police arrived to arrest him.

The military today publicly urged Turkes, generally considered the spiritual leader of the extreme rightist militants in the country to turn himself in to the nearest Army post by 1 p.m. Sunday or face charges of disobeying martial law.

The military junta headed by chief of staff Gen. Kenan Evren has been at pains to show moderation and has proclaimed that newspapers and news agencies would be allowed to function "normally," that is with no censorship. However, the authorities did close down three newspapers -- the pro-Peking Aydinlik, the more orthodox Marxist Demokrat and the Turkes party's newspaper, Hergun, the most virulent of the right-wing press.

The Turkish national press was mostly positive about the takeover, reflecting the general mood of the average Turk. Although hardly jubilant about the latest setback to the country's erratic democracy, many Turks appeared to accept it as a necessary evil to offset the terrorist violence that has killed more than 2,000 people in the country this year.

Turkish radio bulletins today for the first time added the phrase, "president of the republic" to Evren's list of titles, including chief to staff of the republic" to Evren's list of titles, including chief of staff of the armed forces and chairman of the National Security Council.

Evren insisted in a communique today that the military was acting in accordance with an "internal code" that allows the armed forces to intervene, as they have twice before, at times of serious crisis.

Just how great their intervention has been could only be speculated upon in the absence of any real figures or information on just how many persons have been arrested so far. The only statistic issued by the military command came from the martial-law authorities administering the southern port city of Adana. They said they had detained 517 persons in the first 24 hours for curfew violations alone.

The military is known to have made massive arrests of suspected terrorists and their extremist supporters after house-to-house searches in some areas of the major cities where the militants were particularly strong.

An assessment of the overall situation was difficult because of the scant information from the provinces, especially those in the rugged Kurdish cast, where the government extended its selective martial law last year after the Iranian Kurds rose in revolt across the border. Eastern Turkey is an area where both the left and the right maintain strong pockets of support, especially in zones where there has been no real government authority. s

Certainly, the coup was proving benign in the streets of Istanbul. Traffic was somewhat lighter than on normal Saturdays. But along the shores of the Sea of Marmara, on the western outskirts of the city, lovers were strolling arm in arm, young boys were in sunbathing or swimming and the local fishermen's small skiffs were bobbing at work on the oily waters.

"No one is happy about the state of affairs," said one senior editor of Istanbul's middle-of-the-road daily Milliyet. "But I think most people are somewhat relieved that something has finally happened that might curb the violence that has threatened us. The people were fed up with the situation before. Life was simply impossible."

"I think, so far, this has been a gentle coup," said a school teacher watching a casual military patrol move up a sidewalk in the old city. "If it remains gentle, and is brief, it may prove to be for the good."