The Finance Ministry has begun studying details of the punishment to be imposed on Nomura Securities Co. over its shady stock deals and payments to a firm linked to a "sokaiya" corporate extortionist, according to ministry officials.

Japan's biggest securities house will be ordered to suspend operations for a substantial period of time, they said. So far, the stiffest punishment handed out in the industry was an eight-week suspension of operations slapped on Chiyoda Securities Co. in 1996 for compensating favored customers for investment losses.

Industry watchers said Nomura is almost certain to face a tougher penalty because it had already received a six-week suspension of operations for compensation of losses in 1991. The recipient firm, Kojin Building Co., is run by the brother of Ryuichi Koike, 53, who is described as the former head of a sokaiya group. Nomura announced April 22 that Managing Director Junichi Ujiie will assume its presidency May 1 in place of Masashi Suzuki, in a move aimed at improving the firm's public image. "This is the most serious crisis since the foundation of our company," Ujiie told a news conference at the Tokyo Stock Exchange after the announcement. "We would like to rebuild the trust of investors and shareholders. "We must establish a more credible management system based on clear-cut rules, severing ties with antisocial elements," said Ujiie, 51, who was tipped to become president at an extraordinary board meeting earlier April 22. Ujiie, a graduate of the School of Economics at Tokyo University, joined Nomura in 1975, working mainly in the international business field. He became managing director in June 1995.