BONN, JAN. 8 -- Despite major Soviet concessions in principle last August on the key issue of how to verify a proposed agreement to ban chemical weapons, serious and complex differences remain and are likely to prevent the signing of the accord this year, U.S. and West German officials said this week.

The western view is significantly more pessimistic than it was last spring, when delegates to the 40-nation talks in Geneva predicted that the convention could be ready for signing in early 1988.

The new assessment also has triggered a dispute within the North Atlantic Treaty Organization over who is to blame for the delay in progress. West German Foreign Minister Hans-Dietrich Genscher suggested at a news briefing on Monday that the United States and France bear much of the responsibility.

West Germany agrees with the United States that the Soviets, while accepting in principle the need for on-site inspections to prevent cheating on the accord, have been reluctant to spell out details of how such a verification plan should work.

Nevertheless, Genscher made clear that he was unhappy with the resumption by the United States of manufacturing of chemical weapons last month after an 18-year suspension. The United States began producing new binary weapons, using two harmless chemicals that become lethal when combined.

"What is really important now is agreement {in the negotiations} on controls that are as perfect as possible, and not the question of how one can produce new chemical weapons that are as perfect as possible," Genscher said.

The Soviets have warned that U.S. production of chemical weapons could derail the negotiations, although they have pledged to continue negotiating "constructively."

Genscher also criticized what he described as western skepticism over the feasibility of verifying a chemical arms accord, and Bonn government sources said his comments were aimed at the United States and France.

"We see, not without worry, voices now growing louder in the West which raise doubts about whether verification is at all possible in the area of chemical weapons, and this could create new obstacles for conclusion of a treaty," Genscher said.

U.S. officials, responding to Genscher's criticisms, said the United States believes that verification of a chemical arms accord is very challenging and that a foolproof system requires considerable additional work.

"It is an extremely difficult inspection regime," a U.S. official said. "Given all the problems, it seems unlikely" that the accord could be concluded this year, he said.

A western diplomat said Genscher had "gone out on a limb" with his comments and predicted that the United States would not back down.

"Genscher is going to run into a brick wall on this one," the diplomat said.

Genscher considers the issue "quite important" and plans to raise it with Secretary of State George P. Shultz in talks in Washington on Jan. 21, a Foreign Ministry official said.

The United States insists that verification rules be airtight, because chemical weapons are relatively easy to manufacture and conceal.

Soviet Foreign Minister Eduard Shevardnadze removed one of the major disputes, in theory, in a speech in Geneva in August in which he accepted the principle of the need for inspectors to have the right to visit sites where a country believed that a rival might be storing or producing chemical weapons in violation of the planned treaty.

Since then, however, the Soviets have been "parsimonious with the details" on questions such as how much access inspectors would have, a U.S. official said.

The Americans and Soviets also are having increasing difficulty over how to deal with so-called "novel agents," or seemingly harmless chemicals that could be used to manufacture weapons. One of these is Teflon.

Other differences remain, including questions about how many countries would have to sign the treaty before it took effect and how to handle inspections of civilian chemical industries.

Delays in a chemical weapons treaty are particularly unwelcome among the West European allies. They have said the planned scrapping of intermediate-range missiles under the U.S.-Soviet treaty signed Dec. 8 makes it even more important to achieve progress on eliminating chemical weapons.

The Soviets are believed to have a significantly larger supply of chemical weapons than the United States, although Moscow maintains that the arsenals are roughly equal.

One reason for the increased pessimism over prospects for a chemical weapons accord this year is the perception that the Reagan administration has given it a low priority, U.S. and West German officials said.

"Within administration circles, the strategic arms negotiations have a much higher priority than chemical weapons," a U.S. official said.

The administration also is reluctant to overload the Senate with treaties to ratify this year, he said.

"Can you see people throwing this at Congress on top of INF {the Intermediate-range Nuclear Forces Treaty) and START {the expected strategic arms pact}?" he said.

Washington Post correspondent Karen DeYoung contributed to this report from London.