OSAKA — The number of Osaka-based gangsters formally affiliated with Yamaguchi-gumi has fallen to almost half what it was a decade ago. But this may not necessarily be good news for law enforcement officials.

Over the past 10 years, the ranks of Yamaguchi-gumi and its affiliate organized crime groups have dwindled due to a combination of the 1992 antigang law, the prolonged recession and the unwillingness of younger members to undergo years of harsh training, according to local police officials.

However, there is a growing concern among police and the media that future activities of Yamaguchi-gumi will become more difficult to monitor since many of those who leave the gang retain their ties through legitimate businesses.

Earlier this month, Osaka Prefectural Police released the results of a probe that found the total number of Yamaguchi-gumi affiliated gang members in Osaka Prefecture had dropped to about 3,500 — about 54 percent of the estimated 6,400 mobsters whom police believe were active in 1991.

However, the total number of individuals with links to Yamaguchi-gumi — those who provide money or assistance to the gang even if they have not been officially inducted as members — remains about 8,000, the same figure as a decade ago, police said.

"Joining Yamaguchi-gumi has become quite risky because the gang is under strict police surveillance. The don of Yamaguchi-gumi, Yoshinori Watanabe, has made it very clear that the gang should keep a low profile and this has led many members to go underground," one longtime yakuza-watcher in Kobe, who writes for a weekly magazine, said on condition of anonymity.

Police are also stepping up actions against the gang.

During the January-March period of this year, Osaka police issued 100 cease and desist orders against gangs in Osaka Prefecture, 95 of which were directed toward Yamaguchi-gumi affiliated gangs. Most of the orders were issued on allegations of extortion and tax evasion.

On June 6, the day after the regular monthly meeting of the head of the more than 110 gangs affiliated with Yamaguchi-gumi, police raided the gang's Kobe headquarters as well as Watanabe's home on suspicion of violating the firearms control law. No arrests were made.

Some yakuza watchers note that the move came only about two months after one of the gang's most senior leaders was found not guilty of violating the firearms law and released.

While police deny the June 6 raid was politically motivated, not everyone is convinced. Given that it came right after the crime syndicate's monthly gathering, some take it as a sign that authorities are determined to show they will maintain vigilance over the gang.

"This was a highly unusual case," said Tokyo-based writer and yakuza watcher Manabu Miyazawa. "It is rare for the court to find a yakuza member not guilty. The prosecutor (handling the case) may have to resign."

"The verdict has a lot of yakuza wondering whether the raids and pressure on the Yamaguchi-gumi are in retaliation for losing the court case," the Kobe journalist added.

But both police and yakuza watchers agree that, regardless of police activity, Yamaguchi-gumi is continuing to move much of its activity even further underground.

A recent study of Japan's underground economy by Hamagin Research Institute, the research arm of Bank of Yokohama, estimated that illegal income from gang-related activities in Osaka declined from 209 billion yen in 1991 to 143 billion yen in 1998.

Critics of the police, including Miyazawa and lawyers who have represented victims of yakuza-related crimes, said they believe the decline probably stems from falling income in areas like the extortion of small businesses.

Such extortion rackets, compared with the more elaborate schemes involving large corporations, really do not make up a large proportion of today's total yakuza income.

"Although a problem for business owners, petty crimes are committed by lower-level gang members and the amount they take in is small compared with the extortionist tactics and legitimate business of the higher level Yamaguchi-gumi gangs," Osaka-based lawyer Tatsuya Kimura said. "Income from these (relatively small-scale) activities has been decreasing since the advent of the Law for Preventing Gangsters' Unlawful Actions in 1992."

The drop — at least in official numbers — of Yamaguchi-gumi affiliated gang members is also a source of concern for some police.

An officer stationed in the city's bustling Umeda district, who refused to be identified, said fewer Yamaguchi-gumi members means a decline in the flow of information about other illegal activities.

"In the past, there were certain understandings between police and the yakuza, and Yamaguchi-gumi cooperated with the police on occasion, especially if some petty crime was committed by someone who was not one of their members," he said.

"But that has changed, and with the decline in Yamaguchi-gumi members, there is less information being leaked to police than even 10 years ago. It makes it harder, in some ways, for us to crack down on crime."