LIMA, PERU, AUG. 4 -- A major shake-up in the national police force ordered by President Alberto Fujimori has left in its wake uncertainty over what Fujimori's anti-drug-trafficking strategy will be and who will implement it.

On Thursday, Fujimori ordered the forced retirement of more than two dozen police generals, including Gen. Juan Zarate, the head of the national anti-narcotics police unit and the official with whom U.S. officials have worked most closely in the fight against drug trafficking. Also forced to retire were about 70 lower-ranking officials.

It was under Zarate that the anti-drug unit developed a close operational relationship with U.S. Drug Enforcement Administration agents, especially in the Upper Huallaga Valley -- source of most of the world's coca, the plant from which cocaine is made.

In a police force rife with corruption, Zarate has long been regarded by U.S. officials here as an honest official whose commitment in the drug effort never flagged. Moreover, he had developed an officer corps seen as capable and experienced.

"There's no doubt that this is a very serious blow," said a source familiar with the impact of the police reorganization on the U.S. anti-drug program. "They wiped out all his colonels too."

No official reason was given for the removal of Zarate and the other police generals. But an aide to Zarate described the shifts as a power grab for the army, which wants to take a more dominant role in the drug fight -- just as it already dominates the fight against the Shining Path insurgents, seen here as a more pressing problem than drugs.

The army and the police force have long been at odds over issues including the Upper Huallaga Valley, where some army commanders have felt that Zarate's anti-drug activities have worked at cross purposes with the army's mission to defeat Shining Path. The Maoist guerrillas are said to be deeply involved in the coca business in the valley, protecting the growers from police and negotiating with the traffickers and middlemen who buy their coca leaves.

Newly sworn-in Interior Minister Adolfo Alvarado, who is in charge of the police force, is an active-duty army general. He has said he favors a "more integrated" approach in the campaigns against guerrilla violence and drug trafficking, which many interpret as meaning that he wants the army to be in charge.

Peru is a key focus of U.S. attempts to fight the cocaine trade at its source. Officials ultimately hope to be able to use herbicides to destroy the coca fields, which cover as much as 200,000 acres, but the government of former president Alan Garcia refused to allow chemical eradication. Nor has Fujimori made his views clear on the issue, although he too seems unlikely to embrace the use of herbicides.

Working closely with Zarate, the United States financed the construction of a forward base for anti-drug efforts at Santa Lucia in the heart of the Upper Huallaga. The United States also provides funds to equip anti-drug police.

From Santa Lucia, Zarate's forces and U.S. DEA agents have conducted joint raids on processing labs and hidden airstrips. They have also coordinated a slow-moving, on-again, off-again campaign to destroy coca plants by hand, using machines that resemble garden trimmers. American pilots in U.S.-provided airplanes and helicopters keep the base supplied and ferry police and DEA agents.

U.S. officials have complained for years that army officials in the valley are uninterested in the drug fight, and that some have been corrupt.

Zarate could not be reached for comment. An aide said that the police official rumored to be in line to take over as Peru's top anti-drug official, police Gen. Edwin Villacorta, is a good officer but "has no experience in drugs."

A key issue in the police reorganization ordered by Fujimori is the considerable amount of experience that is being lost. "The problem is that the best-trained, most able commanders have been thrown out onto the streets with no rationale whatever," said one government source. "Operationally, this can really hurt the police."

The United States has offered Peru $36 million in military aid -- mostly equipment -- in the drug fight this year, but Garcia never signed the agreement that would allow the aid to begin flowing. Fujimori indicated this week that he looks favorably on the aid, but added, "That is not going to solve the problem of drug trafficking in Peru." He has said he favors an approach that leans heavily toward economic development so that the tens of thousands of people who earn their living from growing coca will have alternative sources of income.

The police shake-up follows other changes in the command structure of the uniformed services that Fujimori has ordered in his first week in office. He had barely been sworn in a week ago before he fired the head of the navy, Adm. Alfonso Panizo. The navy is known as the most conservative branch of the armed forces, and Panizo was rumored to have let it be known that he disliked the idea of a son of Japanese immigrants becoming president.

Asked at a press conference this past week why he had removed Panizo, Fujimori replied sternly, "The president of the republic does not have to give any explanation."