Commercial airliners are filling the skies in ever increasing numbers, causing backups and delays that worry industry officials and leave passengers grumbling in airport waiting lounges.

Industry officials in Europe predict one of the gloomiest summers ever for flight delays as air traffic controllers struggle to allocate slots to a record number of flights in already crowded skies.One of the reasons is the makeup of Europe itself. Unlike the United States, where airspace is controlled by a single aviation authority, European airspace is divided into 34 different parcels, each under different jurisdiction.

At the same time, "the air traffic industry is booming beyond anyone's previous predictions," said Klaus-Ulrich Moeller, a spokesman for West Germany's Lufthansa international airline.

The number of flights is also growing in the Far East, but officials in Japan and Hong Kong, two of the Orient's major commercial air hubs, say the competiton for airspace has not yet reached European proportions.

"During the peak season, booking a seat will be very difficult and planes will be very, very full," said Geoffrey Tudor, a spokesman for Japan Airlines in Tokyo.

But he added that conditions in the Far East were not comparable to the traffic jam in Western Europe's skies.

At terminals throughout Europe, tourists are fuming, business travelers are grumbling and air traffic controllers are protesting.

At England's Manchester International Airport recently, several hundred British tourists recently waited up to 20 hours to get off the ground.

Airport officials rushed 700 extra seats into the airport's waiting lounges and provided clowns and jugglers to keep passengers entertained.

In West Germany, tourists staged a sit-in aboard a jetliner after they were told that their flight, which had arrived three hours late from Majorca in the Mediterranean, could not continue on to Hamburg because the airport there had closed for the night. Airport authorities called in police to remove the passengers.

Lufthansa officials say some of the airline's ground employees have been threatened by angry passengers. Frustrated passengers broke into tears after 23 flights were canceled in one day at Munich's airport, officials said.

Lufthansa spokesman Moeller said the costs of such delays can be staggering for airlines.

He added that Lufthansa jets alone have spent 4,000 hours in holding patterns so far this year over West German airports and estimated that the delays will cost more than $55 million in fuel, wages and maintenance.

"Civil aviation authorities (in Europe) were not prepared for the new surge in traffic," said a spokesman for the International Civil Aviation Organization in Paris. "They had not made investments in new equipment, nor hired or trained personnel."

Many air traffic controllers agreed.

"It is not humanly possible to handle 700 flights within 10 hours as we are asked to do regularly during the busy summer tourist season," said a senior air traffic controller at El Prat airport in Barcelona, Spain.

A delay in England, France or West Germany can cause a ripple effect on runways throughout the continent, controllers say.

The 170-airline International Air Transport Association (IATA) says the gap between the demand for air travel and capacity will continue in Europe unless governments take coordinated action.

"We have airports and airspace capacity which can barely cope with today's demand, let alone tomorrow's," said Gunter Eser, IATA's director general.

According to the Geneva-based association's statistics, international air traffic increased by 13 percent last year and is continuing at that rate this year.

European air traffic also reached 13 percent in 1987 and is expected to increase by at least 7 percent this year. Trans-Atlantic flights, some airline officials say, could jump by as much as 10 percent this year.

Industry officials in Japan say a record number of Japanese are traveling overseas to take advantage of the increased value of the yen.

According to figures compiled by Japan's Narita Aviation Authority, the number of flights to the United States from Japan increased 17.2 percent in 1987 over the previous year.

Flights to Australia and New Zealand increased by more that 31 percent, according to the authority.

Air traffic to South Korea jumped by 12.8 percent and flights to China increased by almost 10 percent, the authority said.

Taipei, a major transit point for many trans-Pacific flights, logged a record 11,244 flights from Hong Kong, a 20.4 percent increase over last year, officials in Hong Kong said.