After a day-long struggle that resembled the storming of a feudal castle, police dislodged a group of students and farmers last night from a fortress-like structure erected to protest Tokyo's new international airport.

Police moved in with fire hoses and tear gas, arrested 36 people, most of them students, and prepared to rip down a tall tower on the fringes of an airport runway that violated aviation safety laws.

At least 22 policemen were injured as protesters inside the concrete-and-steel fortress rained down fire bombs, large rocks, and heavy iron bolts.

The airport, 50 miles from Tokyo in the town of Narita, is scheduled to open late next month. It has been the frequent target of bitter armed protests by farmers, who object to having their land taken for runways, and radical students opposed to the Japanese government. In May police tore down two similar protest towers near the airport.

The protesters have vowed to continue their opposition even after the airport is opened, and one leader has talked of attacking the control tower. Well-organized and highly disciplined in their tactics, the opponents have become a major embarrassment to the government, which had hoped to open the airport years ago as a super-modern gateway to Asia.

The lastest tactic of obstruction was to erect a large, thick-walled fortress near one runway and to man it with armed defenders, most of them students.

Located on private land owned by the opponents, the building had risen to three stories by Sunday night after a feverish weekend of construction work. It was stocked with food and fuel for firebombs in preparation for the inevitable siege.

On Sunday night, it was topped off with a 65-foot steel tower, bringing the entire structure to a height of about 160 feet far above the maximum women who had blocked the roadway permitted by aviation safety law.

Police began their efforts to oust the defenders and haul down the first removing a number of farm tower at daybreak yesterday after by lying down.

Fire trucks shot powerful blasts of water at the fort and local police forces from Tokyo and three other areas moved in with shields and helmets. For most of the day, those inside held them at bay by hurling firebombs and other missiles from ledges inside.

Last night the police let loose with tear gas and finaly penetrated one barricade with the water hoses. They doused the interior an prevented the defenders from igniting their firebombs. Police then scaled the heights on fire truck ladders.

By midnight they had not succeeded in hauling down the tower because a large truck bearing a heavy crane could not set traction in the muddy field.

Police prepared to solve that problem by lining the muddy ruts with iron and concrete. Meanwhile, at least four student defenders clung to their perches high up on the tower, refusing to surrender.