Despite a number of seemingly promising leads and the temporary detention of several suspects, Stockholm police appear to have made little headway in their search for the assassin who shot Swedish Prime Minister Olof Palme three weeks ago.

The release yesterday of a Swede charged only two days earlier with involvement in the killing led to renewed criticism of police handling of the investigation. But a senior police official insisted that while the case "has more dimensions than any other incident that ever occurred in this country," the usual demanding standards of the Swedish democratic and judicial systems had to be respected.

According to sources closely following the investigation, the charge against Victor Gunnarsson, a 32-year-old former member of a right-wing political organization strongly opposed to Palme, fell apart when a key witness near the crime scene failed to identify him. Swedish prosecutors, who take pride in their high rate of convictions, argued that the case against Gunnarsson was only circumstantial and would not hold up in court.

Since the killing on Feb. 28, independent "investigations" conducted by Swedish newspapers have described authorities as slow and inept in dealing with what would be an unusual crime in low-violence Sweden, no matter who the victim.

"The police have more patience than the media," said a police official contacted today in Stockholm . The time for criticism will come after the killer is caught, he said.

"We will deal with it later, when we have time. If we have done something wrong, we will correct it."

Despite allegations of police ineptitude, one popular theory in Stockholm holds that the police know much more than they are telling about who killed Palme and that their apparent bewilderment is part of a strategy to draw the killer out and collect irrefutable evidence. Some proponents of this theory believe that Gunnarsson's release is part of the strategy and that he still may be under suspicion. But an informed western diplomat in Stockholm described the police as "discouraged. They're not quitting, and they can't show it. But they're tired, and they haven't gotten anywhere."

In frequent news conferences, Stockholm Police Commissioner Hans Holmer has divulged relatively little information about the course of the investigation. What has been revealed sometimes has turned out to have been mistaken.

Questions were raised from the earliest days following the shooting, which took place near midnight after Palme and his wife had left a movie theater and were walking on a busy downtown street. Appearing somewhat stunned by the event, police reportedly delayed for crucial hours the setting up of security checks at road, rail and air exits from Stockholm and the country itself.

As police searched in vain for the two bullets fired by the gunman -- one hit Palme, and the other grazed his wife -- both were reported found by civilian bystanders on the sidewalk near the site of the shooting.

Later, Holmer in a news conference described the bullets as "lead-tipped and copper sheathed." That description turned out to be backward, and the bullets subsequently were described as "copper-tipped and lead-sheathed."

Although Holmer said bullets of that type were unknown to Swedish police and could not be found in their reference collection of 600 bullets, local journalists later found them for sale at a store two blocks from the scene of the crime.

Inexplicably, Swedish authorities did not contact international police agencies for assistance in searching for a possible fugitive until several days after the shooting. West German police were not informed until two days after the Swedish Embassy in Bonn received an anonymous telephone call alleging that West German terrorists were responsible for the killing.

Most of the direct speculation about the motive and identity of the killer has come from nonpolice sources. Among the possibilities raised during the past three weeks are members of West Germany's Red Army Faction, Croatian separatists, Kurdish exile extremists and Swedish right-wing militants.

All have had previous run-ins with Swedish authorities and with particular policies or the general socialist ideology of the Palme government. Although Swedish police are known to be investigating all these groups, they have made no direct comment on the results.

No evidence has been uncovered directly linking any of them to Palme's killing. Anonymous claims attributed to the West Germans and Croatians themselves have been disproved or disbelieved, and the Kurdish Workers Party has vehemently denied involvement. The murder weapon, believed by police to be a .357 magnum revolver, has not been found.

Even the arrest March 12 of Gunnarsson, greeted with relief in Sweden, led to more confusion.

In the first week after the assassination, Holmer said that a man running from the direction of the crime scene had been seen by a number of witnesses, ultimately by a taxi driver who saw him jump into a waiting car several blocks away. One of the witnesses provided police with a sketch of the man and Holmer provided the press with a map detailing his escape route through Stockholm streets.

In explaining charges filed against Gunnarsson on Monday, however, authorities outlined a different set of circumstances. Seen running in a different direction, he allegedly stopped a different taxi driver and begged for a ride. The driver, who refused, apparently was the witness who initially identified Gunnarsson from a photograph, but retracted the identification during a face-to-face confrontation.

Police have offered no explanation as to whether their initial scenario and map were wrong, whether Gunnarsson was thought to be the man in the sketch, or whether they had concluded that both of the running men were involved.