Pope Paul's dramatic offer to exchange himself for the 86 Lufthansa hostages before their release yesterday underscored the world's mounting concern over what seems to be an alarming new upsurge in air terrorism.

"If it would be of use, we would even offer our person for the liberation of the hostages," the 80-year-old Pontiff said in a telegram to Joseph Cardinal Hoeffner of Germany.

The governments of the United States, Britain and France had also joined in expressing their dismay over the continuing plight of the hostages, and their support for efforts to end the hijacking.

"This sort of terrorism has got to be stopped," declared British Foreign Secretary David Owen. "We will support (the German government) whatever choice they make."

The State Department also expressed its full support for Bonn. "We understand the incredible dilemma that is represented for any government when terrorists sieze hostages," said State Department spokesman Hodding Carter. "We recognize the extreme difficulty of the decisions the governments involved must make."

French Premier Reynond Barre termed the hijackers a threat to democracy, and called for "the greatest firmness" in meeting that threat. Whatever the bonn government decided, Barre said, would have the "full support" of France.

The concern of other governments over the Lufthansa hijacking reflected the fact that the number of aircraft seizures outside the U.S. has quintupled in the past two years. The Federal Aviation Agency said yesterday that since Jan. 1, 15 successful hijackings have been staged overseas - more than double the seven that took place in all of 1976 and a 400 per cent increase over the three in 1975.

"There has been a definite upsurge," said Federal Aviation Agency spokesman Fred Farr. "We believe it is very closely linked to the upsurge in terrorism around the world generally. Airplanes are a very tempting target."

Most government and airline officials agreed that combating the rising tide of aircraft hijackings overseas would remain difficult as long as security arrangements at foreign airports continue to be spotty. FAA officials noted that in the United States, where standardized security measures have been taken at all airports, only one successful hijacking has occurred since 1972.

"The problem is security measures tend not to be taken quite as seriously in some countries as here," Farr said.

When the FAA noted in mid-summer that the number of foreign hijackings as of July 1 already exceeded the total for all of 1976, it sent out a telegram through U.S. embassies offering to help other countries improve their security. Thus far, 27 countries have taken the FAA up on its offer including West Germany.

Another factor that makes the international fight against hijacking difficult is the continued willingness of a handful of countries to provide air terrorists sanctuary.

"The sanctuaries remain the biggest problem," said John Steele, director of security for Trans World Airlines. Steele, a member of the International Air Traffic Association's Security Advisory Committee, expressed particular dismay over Algeria's decision to give refuge to the Japanese Red Army terrorists who hijacked a Japan Airlines flight in September.

"This was particularly bad," said Steele, "because we had no indication that Algeria would provide a sanctuary."

But the biggest problem, in the view of many experts, is that many successful hijackings are being conducted by a far different type of hijacker than the ones of the 1960s and early 1970s.

The attempts are carried out by small, tightly knit groups of terrorists, carefully trained and ready to give their life for some political cause.

"We're dealing with a different breed of cat," IATA spokesman Don Pengelly declared. "These are determined and desperate people, and they are pretty hard to stop."

A top U.S. government official involved in combating international terrorist activity also cited an increase in the past two years in cooperation between such terrorist groups as Japan's Red Army, Germany's Baader-Meinhof gang, and several Palestinian extremist organizations.

"This certainly is a matter of concern," the official said. "It means a group like the Baader-Meinhof can look to Arab extremists for active cooperation. It gives them allies with different assets, such as access to weapons."

A number of airline officials feel that despite the two recent hijacking spectaculars, airport security around the world has in fact become considerably better in recent years.

"I think there has been a gread deal of improvement," said Steele of TWA, "that's why it's kind of discouraging to see what's been going on. Th effort has been greater than the result would indicate in our mind."