NARITA, Japan - The Japanese government is preparing to deport American chess legend Bobby Fischer for staying in this country on an invalid passport, immigration officials said today.

Fischer was detained at the international airport in this city just outside of Tokyo last Tuesday after trying to board a flight for Manila, Philippines.

Immigration officials, speaking on condition of anonymity, confirmed that Fischer, 61, has been held in their custody since, and said he was being processed for deportation.

Fischer, believed by many to be the greatest chess player ever, has lived in seclusion and semi-secrecy for decades. It remains unclear where he considers home, but after he was taken into custody, friends here said he frequently traveled, staying for short durations in Japan, the Philippines, Germany and other countries.

He was believed to have been in Japan since about April.