Turkey's ruling generals will seek voter approval Sunday for a new constitution that departs radically from the country's past parliamentary structure to establish an authoritarian presidential system.

Acceptance of the constitution also will install Gen. Kenan Evren, who has served as de facto head of state since a September 1980 coup overturned the country's unstable elected government, as president with a seven-year term.

Evren wound up his one-man campaign in favor of the constitution today, warning Turks that its rejection could mean a return to the "national agony"--a reference to the political terrorism that plagued the country until Evren and four other generals took power.

Evren was the only candidate allowed to run for the presidency, and acceptance of the constitution also provides for contining rule by the four generals, who will form a "presidential council."

The government has forbidden campaigning for a "no" vote in the referendum, although opposition to the constitution appears to be widespread because of its hard-line restrictions on the press and civil liberties.

Academics, trade unions and both right- and left-wing press have expressed opposition to the constitution. All of the traditional political parties, which are officially banned by the generals, are campaigning behind the scenes to get the constitution rejected.

The former political leaders are particularly bitter because the constitution bars 100 of them, including former prime ministers Suleyman Demirel and Bulent Ecevit, from political activity for 10 years.

In contrast to the precoup parliamentary system in which Demirel and Ecevit shifted in and out of power, the new constitution increases the powers of the president in such a way as to allow him to appoint and dismiss the prime minister, abolish parliament and delay legislation indefinitely.

Many observers believe, however, that the constitution will be accepted. The government's argument in favor of continued military rule was bolstered by terrorist seizures of the Turkish consulate in Cologne, West Germany, Wednesday and of the Turkish airlines office in Amsterdam today.

In both cases, the gunmen called for rejection of the constitution in the referendum but may have pushed voters in the opposite direction by refreshing memories of the violence here that resulted in up to 20 deaths daily before the coup.

Evren said today that Turkey had won only the "first round" against terrorism. He said that after hovering on the brink of civil war and economic collapse, law and order had been restored. Turks should vote in favor of the constitution, he said, "so that we don't go through those days and years of disaster again, this time, probably, with no hope of salvation."

In the crackdown following the coup, more than 56,000 people have been arrested, about 30,000 of them leftists, according to official statistics. The government is seeking another 7,000 Turks it has accused of being terrorists. About half of the wanted persons are believed to be abroad, mainly in West Germany.

Voting is mandatory, and anyone eligible to vote who fails to register faces a fine and six months in jail. Those who do not vote forfeit their right to vote or hold office for five years, according to rules decreed by the government.

The generals have also banned the sale and use of alcohol on election day.