VISITORS to Tokyo have long marveled at the light security at most government offices, where free access is only occasionally hindered by polite guards, but those days are over for now. The events of the past two weeks have brought an acute sense of caution to the Japanese capital.
After yesterday's assassination attempt against the country's top law-enforcement officer, National Police Agency Director General Takaji Kunimatsu, security was tightened in Tokyo and the government's chief spokesman warned senior officials to take trips only when necessary. Security guards stood in the rain in front of several ministries, carefully questioning anyone who wanted to enter.
Since Mr. Kunimatsu had been leading the investigation into the March 20 release of nerve gas in the Tokyo subway system, speculation immediately arose about possible connections.
An anonymous caller warned several Japanese news organizations that other law-enforcement officials would be injured if police did not halt their investigation into Aum Shinri Kyo, a religious sect that has become the unofficial leading suspect in the subway attack and whose facilities police have searched for nine consecutive days. The group, which has denied involvement in the gas attack, sent out a fax saying it had ''absolutely nothing to do'' with Kunimatsu's shooting.
The official was shot four times as he left his apartment building yesterday morning and was said to be in serious but stable condition last night.
Such shootings are almost unheard of in Japan. Coming on top of the nerve-gas incident, which killed 10 and injured about 5,000 people, yesterday's shooting incident was hard for many Japanese to take.
''These two are first cases,'' says Raisuke Miyawaki, a retired National Police Agency official. ''Police have never experienced them before.''
''We have been better known as a country where attacks of this sort did not occur,'' said chief government spokesman Kozo Igarashi ''We regret this very much.''
Although popular suspicion has turned to Aum Shinri Kyo, whose name means Supreme Truth, Mr. Miyawaki notes that members of Japan's organized- crime syndicates could well be responsible. The shooting ''could be the result of an effective police crackdown on the groups.''
In 1992 the government passed a law that has made it easier for law-enforcement agencies to pursue members of the crime syndicates, known here as yakuza. The crackdown has led to rising incidents of gun violence, as yakuza reorganize and fight for control of criminal enterprises.
Kunimatsu laun- ched a vigorous campaign against gun violence last December saying the country's beloved ''public order'' was in jeopardy. ''I would like you to plan to eradicate armed offenses completely,'' he told a meeting of local police chiefs.
Prime Minister Tomiichi Murayama endorsed the effort last month, and bureaucrats are working on new laws that would penalize anyone caught firing a gun and allow police to watch and arrest people who receive guns by mail from overseas. As it is, Japan bans the private ownership of handguns, but the government seems determined to tighten controls even further to maintain the country's low crime rates.
Police said yesterday that Kunimatsu's assailant had used a handgun and may have fled the scene on a bicycle.
The shooting is certain to increase the already rising pressure on the police to solve some pressing cases. The investigation of Aum has proceeded without any arrests in the nerve-gas incident, and police have seemed unable to locate the group's leader. But some observers have cautioned that Japanese police generally try to compile an irrefutable case before making arrests, with the expectation that the accused will confess to the crime.
The good news is that Kunimatsu, whose appointment to director general last July capped a long and accomplished career, has faced attacks on his person before and prevailed.
In September 1969, when Kunimatsu worked at a police station in the northern part of Tokyo, student extremists bombed his office with a Molotov cocktail. ''I barely escaped the attack,'' he said in a speech he gave when he assumed his current position. ''Though my senior officer scolded me for being careless, I managed to capture the whole group of terrorists thanks to my staff's determined investigation.''
A police officer at the same station, who declined to give his name, yesterday said Kunimatsu had been ''a wise and brilliant police official'' during those years. Then the officer added: ''As he is now.''