Police said Wednesday leftist radicals were responsible for placing two mortars less than a mile from an airport where foreign dignitaries have begun arriving for the funeral of Emperor Hirohito.

"This was done by ultraleftist guerrillas," Narita airport spokesman Kaichi Sato said of the two mortars found Tuesday.The projectiles had no explosive charges except for the propellant and would not have caused much damage, said Sato.

The mortars were placed in a field less than a mile from the airport with a timing device that may have been set to coincide with the arrival of dignitaries, Sato said.

About 7,000 officers have been assigned to protect the airport at Narita, northeast of Tokyo, but they had not been closely watching the farming area where the mortars were set, Sato said.

"Police will begin searching the bushes more carefully," he said.

While some foreign envoys are arriving at Tokyo's New International Airport at Narita, 35 miles east of the capital, President Bush, who arrives Thursday, and most of the other dignitaries will fly into the old airport at Haneda in the southern part of the city along Tokyo Bay.

Security at Haneda also is tight, with police patrolling by land, air and sea. They are using some 75 patrol boats in Tokyo Bay to guard against possible sabotage.