SHIKHANY, U.S.S.R., OCT. 4 -- As the Aeroflot plane banked over the Volga River past the Shikhany military facility, a western military expert took out his camera and, from a seat by the window, calmly started taking pictures of the chemical weapons testing site below.

A year ago, the act would have caused an international incident. Today, no one raised an objection. It was another precedent broken on a historic trip to a Soviet chemical weapons production facility here by a delegation of 110 experts from 45 countries, including six from the United States.

It has been only six months since the Soviet Union, which has the world's largest chemical arsenal, first admitted it even possessed such weapons. This week's unprecedented exhibition at the Shikhany facility, on the central Russian steppe 560 miles southeast of Moscow, is seen as a sign that the Soviet policy of glasnost, or greater openness, is spreading in the military.

"Soviet secrecy was always a big black hole in chemical weapons talks," said Richard Butler, Australian ambassador to a conference on disarmament in Geneva and member of the group in Shikhany. "Now they have colored it gray."

The Shikhany visit followed Soviet leader Mikhail Gorbachev's announcement last April that the Soviet Union has stopped producing chemical weapons and will press for a worldwide ban on them at the 40-nation conference on disarmament.

At a press conference yesterday on board a boat on the Volga River, where the delegation is staying, Yuri Nazarkin, Soviet ambassador to the disarmament conference, said the trip was an answer to "complaints that the Soviet Union is hiding something and hindering progress at negotiations. We have nothing to hide."

During the last two days, the Soviet Union put on display 19 different types of chemical munitions, ranging from a 10-foot warhead for a tactical missile to a half-pound hand grenade.

Today, Soviet soldiers gave a three-hour demonstration of a mobile decontamination unit, experimenting on two rabbits, one of which died seconds after being injected with a lethal dose of the toxic agent sarin. A quantity of the sarin was then mixed with other chemicals to render it harmless and injected into a second rabbit, which seemed to suffer no ill effects.

The trip underscored the horror of chemical weapons -- from the mustard gas used in trenches in World War I to toxic agents with names such as sarin, soman, VX and CS -- which choke or burn people before killing them.

Soviet spokesmen here said current U.S. plans to start chemical weapon production on Dec. 1 after an 18-year hiatus were "contradictory" to progress being made at the Geneva talks.

This summer in Geneva, the Soviet Union removed a key obstacle to an agreement on a chemical weapons ban when it dropped objections to 48-hour challenge inspections, considered an essential safeguard.

Col. Gen. Vladimir Pikalov, head of the chemical corps in the Soviet Defense Ministry, said he thought an agreement could be reached in Geneva this year, but western observers said a number of complex issues remain to be resolved. An estimated 15 countries now have chemical weapons.

The Shikhany trip, announced in August, was hailed by most western specialists as an important first step by the Soviets toward more openness. But several visitors noted that their hosts did not answer a number of important questions, such as the size and location of Soviet stockpiles.

When asked to give the size of the Soviet arsenal, estimated in the West at 300,000 tons of toxic agents, Lt. Gen. Anatoly Kuntsevich said the "theme of the briefing is not connected with stockpiles."

Some delegates also noted that the chemical munitions displayed were outdated. "I think what we have seen here was sort of like a tour of a museum," said Max Friedersdorf, U.S. envoy to the Geneva conference. "I would say that on a scale of one to 10, it is probably a one or two on confidence-building."

Skepticism about the completeness of the Soviet display was confirmed when Kuntsevich told a press conference that some "modernized types" of standard chemical weapons had not been shown. He stressed however, that the Soviet Union has no weapons that other countries do not have.

Although they said the trip provided little new information, most western experts said they were pleased with the results. "The major impact is psychological, for them, not for us," said one Scandinavian delegate.

For two days, this facility was turned inside out for the benefit of the visiting guests. Closed roads were opened with soldiers standing stiffly at attention along the route; tents were erected offering fresh fruit and pastries, tea and schnapps; guests were provided with gas masks, raincoats, jackets and hardhats; and most importantly, rules prohibiting photography and sound recording were suspended.

The delegation, which also included 55 members of the Soviet and foreign press, flew to a nearby military air base in four airplanes. Members were transported to the chemical test site in six buses and housed 12 miles away on a luxurious liner on the Volga River.

Descending onto a Soviet military base, traditionally the most forbidden of the Soviet Union's many closed zones, the foreigners were at first tentative in trying their new freedom. By the second day, however, Pentagon experts and their NATO counterparts were busy photographing everything from air control monitoring systems to the insides of Soviet gas masks.