Early rising Japanese riot police scored a bloodless victory over diehard protesters today and brought a long-delayed new airport for Tokyo appreciably closer to opening.

The operation began before dawn. On a coded radion signal, 2,000 police moved on Narita Airport while workmen felled two towers that symbolized enviromental opposition to its operation. The 100 and 200-foot tall steel towers stood on the approach to the 10,000-foot main runway and prevented planes from taking off or landing.

Forty miles east of Tokyo, Narita has been a nightmare construction project since work started in 1966. A coalition of farmers and student activists has conducted a fierce resistance with arrests and injuries over the years running into thousands.

Narita is needed to relieve heavy traffic pressure on the existing Haneda Airport. Additionally, the delays have caused prodigious expense. The airport, complete down to hotels, exployee housing and computerized arrival boards, has cost $2 billion and is running up deficits of $100,000 a day while it sits, used only by birds.

If the airport can open this year as authorities jubilantly predicted following today's police action, it will be six years later than scheduled and four years after construction was completed. Substantial obstacles remain, however.Citizens opposition has stalled construction of jet-fuel pipeline to the airport and a rapid transit link to Tokyo.

Trouble began 11 years ago when the airport authority announced its plan without first securing agreement from farmers who owned the land. In 1971, police and demonstrators armed with staves and molotov cocktails fought a pitched battle over the ouster of farmers from the site. Three police officers died in the melee.

Since then, the police have sidestepped direct confrontation. They struck today two days after a court ruling permitting removal of the towers. Yesterday was a press holiday in Japan so newspapers could not leak the police tactics in advance. The resistance groups recently "fortified" the towers with plywood and announced plans for an epic defense. The seven surprised students found inside did not resist the police, and a small group of farmers was heavily outnumbered.

A spokesman for the Anti-Airport League said: "They really behaved in a treacherous manner. Now we don't have to obey any kind of law. We can do what we want."

This afternoon three ultraleftist radicals briefly occupied the airport authority offices in Tokyo and flew their group flag through a broken window pane. They shouted, "Down with Narity Airport," as police took them away.

"The loss to the nation was recognized by the court and the Japanese public," said Shigeru Otsuka, president of the Tokyo International Airport Authority.