It is the time of eventide when, as Thomas Hardy put it, "darkness had to a great extent arrived hereon, while the day stood distinct in the sky." The time of day, in other words, when one is wondering whether to put on the lights now or a few minutes later on the way to the kitchen for a refill.

Nowadays, in my part of the Turkish capital--and in parts of 20 other provinces where about half the population of 45 million people live--one need not luxuriate in such idle rumination. Precisely at 7 p.m. the one-hour power cut plunges half of Ankara's population of 2 million into darkness.

In the other half of the city the power cut starts at 9 p.m. and, with luck, ends at 11. This is called "taking darkness for a walk," which means that power is cut at different parts of the country at different times. Elevators freeze in midair, refrigerators stop with a shudder, factories grind to a halt and people start bumping into things. Street lights, traffic lights, neon lights and telexes die. Telephones start behaving oddly. Faucets run dry and radiators go cold.

IT IS A MELANCHOLY hour (in fact, it often lasts much longer than an hour) for many except candle manufacturers, who must have been rubbing their hands since the electricity authority announced the power cuts earlier this month.

It means that summer has come to an end and, with winter around the corner, the need to economize on electricity has begun once more.

This is despite the fact that 40 percent of the people living in rural areas have no electricity at all. Overall, Turks consume less electricity per capita than any other people in Europe.

Electricity output in 1980 fell more than 30 percent below estimates of the nation's estimated "potential demand." To make up the deficit, the electricity authority was forced to order daily power cuts of three hours--two in daytime and one at night.

The only province to escape the blow was Hakkari, a poor mountainous province of 100,000 people stretching along the borders with Iran and Iraq, where little electricity is used anyway.

THE DECISION did not take anybody by surprise: power cuts have been a part of the colder half of the year in Turkey for the past two years, like autumn leaves, chestnuts, and snow. In 1979 the routine daily power cut lasted five hours.

Turkey imports 80 percent of its crude oil but has vast hydroelectric potential and rich fields of soft coal. But only a small part of this indigenous potential is being utilized because of lack of funds and years of bad planning and management. According to an estimate, only 10 percent of hydroelectric potential is being used. No new plants have gone on stream during the past two years, a period during which Turkey was nearly torn apart by government crises and political terrorism.

Next month, output will increase slightly when two new units are hooked into the system. The electricity authority said that when this happens it will "review" the nocturnal power cuts.

Industry, which is consuming nearly three-quarters of the electricity output, is recovering from a three-year depression.

Demand from industry, even though it is only working at 55 percent capacity, has risen by 18 percent so far this year.

The new military administration has given power projects top priority. It is attaching particular importance to the Afsin-Elbistan project in eastern Turkey. When completed, this will become the largest soft coal-powered thermal power plant in the world, generating 7.8 billion kilowatt-hours per year.

After years of neglect, the country has a lot of catching up to do, quickly, both as a social service and for industry.