Mehmet Ali Agca is in the news here again, but not as the would-be assassin of Pope John Paul II just two years ago. The Turkish government has reopened the case of Agca's first victim, the murdered crusading editor Abdi Ipekci.

The government acted after investigative reporter Ugur Mumcu presented a carefully documented picture of cozy cooperation over a number of years among Agca's guerrilla group, the Gray Wolves, the right-wing National Action Party, Turkish smugglers and Bulgarian officials.

These allegations could help shed light on international criminal circles closely related to those being probed in Italy by magistrate Ilario Martella in his investigation of the papal shooting. He has charged four Turks besides Agca--all with ties either to the Gray Wolves or Turkish crime circles--and three Bulgarian government employes with complicity in the attack.

Mumcu, a former law professor who studied thousands of documents and interviewed hundreds of sources in his inquiry, said in an interview here that he remains convinced editor Ipekci was killed because he was preparing to investigate smuggling and corruption in Turkish customs.

Bulgaria has been shown to have played a major role in massive smuggling into Turkey that flourished for more than a decade in goods ranging from guns and drugs to coffee, raw materials and spare parts.

Mumcu's investigation thus suggests one way Agca may have been brought into contact with the Bulgarians, through a network of groups interested in protecting their smuggling operations.

Turkish smugglers and extremist political movements have been linked in the past to Bulgaria. Turkish secret service documents assert that Bulgaria was the source of thousands of arms smuggled into Turkey for paramilitary organizations engaged in virtual civil war in 1980-81. The documents suggest that Bulgaria actively sought to destabilize Turkey, the strategic anchor of NATO's eastern flank.

International media and political opinion have considered Bulgarian and possibly Soviet involvement in the papal shooting to be plausible because of the pope's active support for the now-banned Solidarity trade union in the pontiff's native Poland. It also appears reasonable that the Gray Wolves, and hence Agca, could have played a role as "hit men" for the Bulgarians because of the Wolves' links to Turkish political and criminal circles in turn tied to the Bulgarians.

But the evidence of links between these groups still falls short of establishing that the papal shooting was ordered from Bulgaria or Moscow.

Mumcu, however, has uncovered a collection of threads that could link Agca to one of the Turks charged by Martella in the papal shooting. He is Bekir Celenk, alleged by Turkish intelligence documents to have been a major smuggler in arms and other contraband and to have had Soviet Bloc connections.

Based for several years in Geneva, Celenk now is being held by Bulgarian authorities in semidetention in the capital of Sofia. He allegedly was the source of an offer to Agca of about $1.75 million in West German marks to shoot the pope.

Mumcu also alleged that Celenk worked for Abuzer Ugurlu, now jailed in Turkey on charges of being a top Turkish crime boss. Other Turks in Western Europe also have been linked to Ugurlu, including Omer Mersan. He allegedly provided Agca with a pilfered passport and spoke with him repeatedly on the telephone, once shortly before the assassination attempt in St. Peter's Square.

The Bulgarian government has suggested that western intelligence agencies including the CIA somehow have planted the story of the "Bulgarian connection" in the papal shooting as part of a disinformation campaign against the Soviet Bloc. In a letter to the French daily Le Matin in January, the Bulgarian Embassy in Paris referred to allegations that the Wolves may have had links with the CIA. The letter referred to insistent reports recalled by Mumcu and others of the Wolves' relations with an alleged CIA agent named Ruzi Nazar. A Turcoman born in the Soviet Union, Nazar deserted the Red Army in World War II and fought for the Nazis, according to several reports. He is alleged to have been recruited by the CIA and worked for many years in Turkey. He is said to be living under an alias somewhere in Germany.

Mumcu carried out his journalistic inquiry in an effort to reopen the investigation into who was behind the first shooting in Agca's career as a self-proclaimed "international terrorist," his Feb. 1, 1979, murder of crusading editor Ipekci.

Mumcu worked with the fervor of a latter-day Emile Zola determined to reopen the Dreyfus affair in France in the late 1800s. His achievement in single-handedly getting the government to reopen the Ipekci case was all the more noteworthy because the generals who run Turkey today view Agca, Ipekci, the Gray Wolves and smuggling as things of the past.

Turkish officials say they are satisfied that the once-massive smuggling has stopped, partly because of the clampdown following the September 1980 military takeover and in part because of an apparent backing off by Bulgaria itself. The Turks have been embarrassed by Agca's notoriety springing from the papal case but also have used it to bolster their claims that martial law was necessary to halt Turkish terrorism.

In seeking to play down the attention paid to the papal shooting, the Turkish officials left unsaid the advantage for the government of avoiding a raking up of the past that could heighten tensions with Bulgaria. The neighboring Communist state may not be in a position today to undermine Turkey but certainly could create problems.

Bulgaria is the land-bridge for the more than 2 million Turks who each year go back and forth between their homeland and Western Europe. Bulgaria also provides a sizable amount of Turkey's electric power, and a Turkish minority of about a million lives in Bulgaria.

"Why should we recall that the Army seized more arms than it itself possessed--many of them smuggled in from Bulgaria--now that law and order has been restored?" one Turkish official said.

In Italy, magistrate Martella is working under a mandate from an Italian court to probe what it called "a complex plot orchestrated by hidden minds interested in destabilization." Little has emerged regarding possible links between the five Turks and three Bulgarians whom he has charged in the papal shooting.

Two of the Turks, both alleged Gray Wolf couriers, currently are in Italian prisons like Agca awaiting Martella's decision on whether to order them to trial.

One of them, Musa Cedar Celebi, allegedly conveyed Celenk's offer to Agca of cash to shoot the pope, according to Italian and other foreign sources. The other, Omer Bagci, is alleged by Martella to have left for Agca the powerful Browning automatic pistol that seriously wounded the pope in the abdomen, arm and hand. Bagci was charged with leaving the weapon in a Milan railway station baggage locker.

The magistrate successfully extradited Celebi from West Germany and Bagci from Switzerland. Both countries are home to large Turkish exile communities.

The other three Turks named by Martella are Agca himself, Celenk and Oral Celik, who also is wanted in Turkey for allegedly helping Agca to escape from a high-security Turkish jail where he was serving time for the Ipekci murder.

Mumcu alleges that the right-wing National Action Party (NAP), led by Col. Alpaslan Turkes, had established close working relationships with corrupt Turkish customs officials, including former customs minister Tungay Mataraci, who since has been sentenced to 36 years in prison by a military court.

What is less clear is the hierarchy of relationships linking criminal circles, the Bulgarians and the Gray Wolves.

By all accounts Agca was a second-string Gray Wolf, unlike the other two accomplices in the Ipekci murder, Mehmet Sener and especially Oral Celik.

But although use of such Gray Wolf enforcers at first glance would indicate that the highly disciplined organization was working for the Turkish mafia, some Turkish officials wonder if it was not Turkes and his lieutenants who were calling the shots.

These officials remember Turkes' period in government and the pervasive influence his NAP exercised throughout the state machinery until the military takeover.

"It was worth your life to walk in the streets before September 1980," a Turkish diplomat recalled, "especially if you were at all involved in politics. The Gray Wolves were that powerful." Mumcu himself was assigned two police bodyguards during that period.

Moreover, in a series of densely documented articles earlier this year in the newspaper Cumhuriyet, Mumcu repeatedly suggested that it was the NAP's influence that prevented elementary police and judicial coordination and follow-up procedures in the Ipekci case.

Similarly, the stolen passports used by Agca and other Gray Wolves implicated in the Ipekci and pope cases were procured from Nevesehir, a district notorious for Gray Wolf influence before September 1980.

Several key Gray Wolves involved in the Ipekci murder reappeared once Agca escaped in November 1979 from a high-security Turkish prison--with Gray Wolf help--and turned up in 1980 in Bulgaria traveling on a fake Indian passport issued in the name of Joginder Singh.

If nothing else, Agca and the other Gray Wolves and the Turkish mafia stuck together, using safe havens in Bulgaria and elsewhere in Europe once Turkey under military rule became too dangerous for them.