International terrorism, growing 12 percent to 15 percent a year, has almost become an accepted institution, according to a Rand Corp. analysis. It also finds a nuclear terrorist incident unlikely.

Brian M. Jenkins, the California think tank's chief analyst for terrorism studies, said the trend toward state sponsorship of terrorism will continue and could lead to "a new kind of global guerrilla warfare" in which terrorists launch operations from "badlands" nations and retreat there afterward.

The study, "The Future Course of International Terrorism," is excerpted in the December issue of Jenkins' Terrorism Violence Insurgency Report and says that terrorist tactics "have become a routine way of focusing attention on a dispute." As in all disputes, it says, "a semipermanent infrastructure of support has emerged," providing connections, alliances, safe houses, arms, counterfeit documents and other services around the globe.

"To a certain extent, international terrorism has become institutionalized," Jenkins wrote. Since the 1972 attack on Olympic athletes in Munich, he said, terrorist incidents have risen at an annual rate of 12 percent to 15 percent, last year involving terrorists and victims from 60 countries. The study indicates that the incidents increasingly involve large-scale, indiscriminate violence, such as bombs detonated in public places.

In an interview, Jenkins said "the most insidious trend" is toward public indifference. "Terrorism is becoming commonplace -- ordinary, banal and therefore somehow tolerable . . . . Extraordinary security measures no longer attract any comment. We expect diplomats to be assassinated and states to be involved."

He added that measures to combat terrorism could cause "a lot of bumping and shoving around the Fourth Amendment" to the U.S. Constitution, which prohibits unreasonable search and seizure.

A State Department official expressed general agreement with Jenkins' report and called him "highly respected" in terrorism studies.

The report said terrorists' tactics and targets will probably not change much. "Terrorists blow up things, kill people or seize hostages. Every incident is merely a variation," Jenkins wrote. Although attacks on data-processing systems, electrical energy networks and nuclear reactors have occurred and will recur, they require sophistication and persistent follow-up to be effective and lack the public drama of a hostage-taking.

"Terrorists want a lot of people watching, not a lot of people dead," Jenkins said.

Nuclear terrorism "is neither imminent nor inevitable" because of technical reasons and because it involves mass murder, an idea that would split a terrorist group and expose it to betrayal, he said. Some terrorists would oppose it on moral grounds or because nuclear events would provoke public revulsion and government crackdowns.

"Certainly, in the face of a nuclear threat, the rules that now limit police authorities in most democracies would change," Jenkins said.

Similarly, chemical and biological weapons involve uncontrollable mass killings that are less useful to terrorists than to governments at war. "If chemical warfare becomes more commonplace," Jenkins wrote, "we cannot dismiss its potential use by terrorists. The same is true of nuclear weapons, but probably over a longer time period."

The Middle East will remain a focus of terrorists, in part because of religion. "As we have seen throughout history, the presumed approval of God for the killing of pagans, heathens or infidels can permit acts of great destruction and self-destruction," Jenkins wrote.

If the Iranian revolution and its spread to Lebanon become a model for other Third World nations, he said, "We are in for a lot of trouble."