NEWS ANALYSIS : Rapid Change Creating Mideast Power Shift : Politics: Hostage’s freedom reflects the new order. But other events underscore the opposition to it.

The release of British hostage John McCarthy in Beirut on Thursday was the result of kaleidoscopic political changes in the Middle East over the last year that are creating a new balance of power.

But the reported abduction hours later of a French national in Lebanon and the assassination less than a day earlier of Iranian opposition leader Shahpour Bakhtiar in Paris underscore the volatility of that new order and the opposition to it, according to U.S. officials and Middle East analysts.

While U.S. officials remain cautiously optimistic that an American hostage will be released, counterterrorism experts predict that the next phase of the hostage drama will be determined by whether the forces shaping the new order in the three most troubled Middle East nations are capable of fending off the “spoilers” and hard-liners.

Several factors have come together to alter the political climate that has made hostage abductions the most cost-effective terrorism tactic since the late 1970s:

In Lebanon, a new government is gradually restoring law and order and disarming militias that created anarchy for 16 years, squeezing renegade groups such as Islamic Jihad, which held McCarthy, along with the broader Hezbollah movement.

In Syria, a facilitator in most recent hostage releases, the government’s warmer relationship with the United States during and after the Persian Gulf War and the declining influence of the Soviet Union have created a new pragmatism about dealing with the West--and its priorities--especially on what may be the eve of U.S.-orchestrated peace talks on the broader Arab-Israeli dispute.

And in Iran, which U.S. officials believe provided the main impetus for McCarthy’s release, the post-Khomeini regime wants to exploit the new post-Gulf War climate--in which Iraq replaced Iran as the region’s leading pariah. Tehran wants to win the kind of credit, technology, expertise and respect from the West that would help rebuild the war-ravaged nation and its tattered economy.

The standing of the United States as the unchallenged influence in the region also has given a much-needed boost to longstanding efforts to end the hostage saga, which began in Lebanon, ironically, with the 1982 abduction of four Iranian diplomats.

“This is a consummation of a lengthy process in which the atmosphere surrounding the hostage-takers has changed,” said Clovis Maksoud, a Lebanese academic and former Arab League representative to the United Nations and the United States.

Most of the main players now have an interest in freeing the remaining Western hostages, believed to number at least 10, some of whom have been held more than six years.

But not all players are yet “on board,” said a U.S. counterterrorism expert. A minority of hard-liners and “spoilers” apparently is trying to undermine the evolving new order and any government perceived to be warming up to the West.

Their motives often are related as much to internal politics--especially in Lebanon and Iran--as to the hostage issue.

“There are still plenty of interests in Lebanon that do not want stability restored because it means they’ll be frozen out,” said Bruce Hoffman, a terrorism specialist at the RAND Corp. think tank in Santa Monica. “Hostage-taking is a last-gasp means of trying to have a say in Lebanon’s future.”

Bakhtiar’s assassination “was calculated, like the kidnaping, to wreck or scuttle a new modus vivendi between Iran and the West. It sends a message that (hard-liners) will not give up. It still shows the power of radical elements, not to wrest control of power, but to spoil any arrangement Tehran wants to make with the West,” he added.

There are as yet no claims of responsibility for the stabbing murder of Bakhtiar, the last prime minister of the late Shah Mohammed Rezi Pahlavi before the monarchy was toppled by revolution in 1979. But U.S. counterterrorism sources linked it and the apparent abduction in Lebanon of French national Jerome Leyraud to McCarthy’s release. “It’s all part of the same picture,” said one U.S. official.

Both the assassination and the abduction have important foreign-policy implications in Europe and the Middle East.

France, along with Germany, was actively engaged in an effort to bring Iran back into the community of nations. In what was widely viewed as a “no-deal deal,” Paris last year freed five men sentenced to life imprisonment for a failed 1980 assassination attempt on Bakhtiar after the release of the last French hostages in Lebanon. The two nations also were in the final throes of working out the settlement of a billion-dollar loan made to France during the shah’s rule.

This fall, President Francois Mitterrand is scheduled to visit Tehran. That trip is to be followed by a reciprocal visit to France by Iranian President Hashemi Rafsanjani. If it takes place, it will be the first official trip by an Iranian chief of state to the West since the 1979 revolution that installed a clergy-led regime in Iran.

But the Bakhtiar assassination in France and the abduction of Leyraud, if confirmed, are almost certain to sour the budding relationship, U.S. counterterrorism officials predicted.

The spoiler tactic is a classic one. Iranian hard-liners leaked word of the secret 1986 visit to Tehran of former National Security Adviser Robert C. McFarlane to undermine the pragmatic faction led by Rafsanjani.

“It’s the same pattern,” said Hoffman. “(Hard-liners) wait until the moment they can to do the utmost damage. Just as the world and the pragmatists think they’re making progress in developing relations, the spoilers emerge at the worst possible time.

“They’re serving notice on moderates and pragmatists that there will be a radical element to spoil or wreck any deal. It’s also a reflection of their power, that they refuse to go away.”

Spoilers could undermine the new efforts to free other hostages. “We had warned against releasing any hostage,’ said a communique released by the Organization for the Defense of Prisoners’ Rights, which claimed responsibility Thursday for the abduction of Leyraud.

“We shall not stop at this point if the deals and the trading persist at the expense of the dignity of our brethren imprisoned in Israel and the political prisoners in the West.”