Fortified by widespread public support, Turkey's military rulers are pushing ahead with controversial measures to purge key institutions before returning the country to formal civilian political control this fall.

In recent months, Gen. Kenan Evren's government has weeded out leftist university professors, closed newspapers, tightened press censorship and moved forward with mass trials of labor leaders and other prominent Turks.

The drive to restrict political dissent lies at the heart of what Evren calls the "third blow" to eradicate the abuses that had reduced Turkey to near anarchy and economic desolation before he seized power in September 1980.

The first two blows were the military takeover--the third in as many decades--and the overwhelmingly approved referendum last November endorsing a constitution with a centralized American-style presidency.

Evren's current drive seems designed to put his personal stamp on as much as possible before the start of the campaign for elections tentatively scheduled for Oct. 16.

In the first step toward elections, the military Sunday lifted a 22-month ban on political activity and announced a law governing the formation of political parties, news agencies reported. The new law bans students, teachers, judges, prosecutors, the military and civil servants from participation in political parties and bans about 100 former politicians from political activity for the next 10 years, United Press International said.

No old parties may be revived, and new ones must submit their party manifestoes to the government May 16.

Martial law, in force in many cities and provinces for two years before the 1980 coup applied it nationwide, will be lifted during the election campaign. The presence of armored vehicles and troops, much in evidence in cities for months following the coup, has been greatly reduced.

Evren and his military colleagues are widely expected to emerge as the dominant force in the new parliament. In the view of many observers, this is as much because of their genuine popularity as the government's control of state-run radio and television.

Increasingly cloaking himself in the mantle of Mustafa Kemal Ataturk, the revered founder of modern Turkey, Evren has proven himself a capable leader, many observers say. Some critics, however, would prefer that he remain more aloof and statesmanlike rather than involve himself in the rough and tumble of everyday politics.

His down-to-earth approach has touched many sophisticated Turks as well as the humbler citizens relieved at the country's return to law and order. A woman professor said that she caught herself watching Evren on television and imagining that he would step out of the set and ask her to prepare a cup of coffee "like an authoritarian uncle."

Although since Ataturk's day the Army has been a force for modernization--against Moslem religious leaders and the merchant and landlord class--some Turks fear that this time the military does not intened to leave politics but just to exchange its uniforms for business suits.

Increasingly, Evren has placed military men, some only recently retired, in key government and civil service positions. His prime minister, former admiral Bulend Ulusu, is expected to head a new right-of-center political party.

Evren's current crackdown appears to have caused more widespread criticism abroad--especially in Western Europe--than at home where many Turks appear grateful to the military for having improved the economy and all but stamped out terrorism, which once claimed as many as 30 lives daily.

Since martial law was introduced in December 1978, 23 of 114 men condemned to death for political murders have been executed, and 29,940 men have been sentenced to prison terms ranging from five years to life, according to recently published official statistics.

Since his November referendum victory, Evren has purged about 40 university professors, mostly in law, political science and economics, and failed to renew the contracts of nearly 200 others. About 300 others have retired, a move that allows them to reapply for teaching and other public service posts under a civilian government.

Although his weeding out of the faculty--there are more than 13,000 teaching posts in 19 universities--has angered many Turkish intellectuals, it has proven popular with parents who remember the disorders and violence of pre-1980 campus life.

Press censorship has become increasingly rigorous despite the vigorous efforts by Turkish journalists to get around a ban on political commentary by discussion of theoretical problems facing the nation.

Cumhuriyet, the respected left-of-center newspaper, was temporarily shut down for republishing a more than 20-year-old editorial that the military government disliked. Its publisher, Nadir Nadi, is on trial, and his case is to be resumed early next month.

All these developments have prompted increasing criticism from Europeans, especially in the Netherlands and Scandinavia, who look askance at civil rights violations including hundreds of alleged cases of torture. On the other hand, some suspected torturers have been arrested and brought to trial.

The parliamentary assembly of the Strasbourg-based Council of Europe in January voted overwhelmingly to ask Turkey to refrain from voting in its meetings until democratic rights were fully restored.

The U.S. government has made known its concern but refrained from withholding aid as West Germany did last year with a $200 million grant.

Instead, the United States and some other conservative western governments have preferred to stress that Evren has kept his word so far about planning to return Turkey to civilian rule.