The drive by a Spanish magistrate to extradite former Chilean president Augusto Pinochet from Britain and try him on charges of genocide, terrorism and torture has thrown the Spanish legal establishment into confusion and placed Prime Minister Jose Maria Aznar in a delicate political position.

The crusade by Baltasar Garzon, Spain's best-known investigating judge, is widely supported by Spanish public and media opinion. All major left- and right-wing newspapers favor the attempt to bring Pinochet to justice in Spain for the torture, deaths or disappearances of 94 people during his 17-year rule in Chile.

But Spain's chief government-appointed prosecutor, Eduardo Fungarino, earlier this week filed a court motion asserting that Garzon, and Spain, do not have jurisdiction over the alleged crimes because they were not committed in Spain.

In fact, Garzon's order of international arrest for Pinochet does not name a single Spaniard killed as part of Pinochet's regime of oppression. Rather, nearly all are Chileans or Argentines kidnapped or killed in Argentina.

Garzon, one of a corps of independent investigative magistrates under the Spanish judicial system, has indicated his interest in 3,000 of the people who disappeared under authoritarian rule in Chile and Argentina in the 1970s and 1980s, and he has a separate investigation underway into the Argentine incidents.

As Chilean president from 1973 to 1990, Garzon's arrest order said, Pinochet was "the leader of an international organization created . . . to conceive, develop and execute the systematic planning of illegal detentions {kidnappings}, torture, forced relocations, assassinations and/or disappearances of numerous persons, including Argentines, Spaniards, Britons, Americans, Chileans and other nationalities."

Fungarino cited "an absolute lack of jurisdiction" when he appealed Garzon's extradition request Monday, and said Garzon had not followed correct legal procedures. Pinochet, 82, was arrested in Britain on Friday. The retired general remains sequestered at a London clinic, where he is recovering from back surgery, pending the outcome of the extradition request.

According to Juan Garces, a lawyer for an association of families whose relatives perished under the Pinochet regime, "the law is crystal clear." He cited a 1984 Spanish law that bestows unlimited jurisdiction in international crimes: genocide, terrorism, counterfeiting, prostitution, piracy and drug-trafficking.

"The law is so clear that we expect a solemn reaffirmation of it by the court," he said.

A nine-judge panel of the Spanish high criminal court is expected to rule on the Fungarino motion late next week. If the prosecutor is upheld, the case is likely to stop there because appeals possibilities are limited. If Garzon wins, he has 40 days under international law to present his extradition request.

He will surely move forward if he can. Garzon is one of the best-known of a young generation of investigating magistrates in Spain and France who are delving into governmental corruption and wrongdoing. He is politically a Socialist and once held elective office.

After quitting politics, he turned to justice, targeting members of his own side as well as former dictators. He was peripherally involved in investigations of anti-Basque terrorism during the Socialist government of prime minister Felipe Gonzalez, as well as Spanish corruption and drug trafficking, and has pursued political killings in Argentina as well as Chile.

"Whenever there is a cause celebre, he is always there," said Miguel Angel Bastenier, deputy editor of El Pais newspaper. "He loves to be in the limelight. But that doesn't mean he's not a solid professional."

However, it is Aznar's center-right government that must decide whether to transmit the extradition request to British authorities. Aznar and other members of his Popular Party government know that Spaniards are strongly in favor of extraditing Pinochet. But they also know the importance of Spain's economic relations with Chile, which opposes extradition. The opposition Socialist Party, with none of the nuances of governing to consider, openly favors extradition.

Spanish companies have a 21.7 percent share of foreign investment in Chile, the largest of any nation. British companies have the second-largest with 21.5 percent. Telecommunications, banking and defense are areas of close business cooperation.

"Spanish public opinion is in favor. The only problem is the interests of Spanish firms in Chile," said one former government official.

Aznar has said the affair is a matter of justice and that the judicial process should operate independently. On Tuesday, in a vaguely worded answer at a news conference, he said he would follow the will of justice, implying he would not block the extradition request if the high court found for it. British Prime Minister Tony Blair also was quoted today as saying "it is a judicial process." In an interview with representatives of six foreign newspapers, including El Mundo in Spain, Blair said extradition "cannot be a governmental decision because that would be interfering in our justice system, which we cannot do."

Also today, 36 U.S. members of Congress wrote President Clinton, asking the United States to turn over privileged information requested by Garzon on Pinochet's alleged international criminal activities. The best-known of those activities in the United States: the 1976 car-bomb deaths of Chilean exile Orlando Letelier and his assistant, Ronni Moffitt, while they were driving around Sheridan Circle in Washington. CAPTION: BALTASAR GARZON ec CAPTION: JOSE MARIA AZNAR ec