The House voted yesterday, 216 to 202, to deny President Reagan $115 million he sought to begin production of nerve gas for the first time since 1969.

It was the first and may be the only Reagan defeat this year on a major weapons program.

House Armed Services Committee members and administration officials, including Secretary of State George P. Shultz and Defense Secretary Caspar W. Weinberger, had lobbied strenuously for the funds, saying the Soviet Union will not negotiate a ban on chemical weapons unless the United States modernizes its arsenal.

Despite the 26 seats the Democrats gained in the House last year, the victory margin was less than half that rolled up by opponents of chemical weapons in July, 1982. The earlier vote, when Reagan first requested a resumption of chemical weapon production, was 225 to 192.

"They worked awfully hard this year," Rep. Ed Bethune (R-Ark.), who led the fight against production, said of the administration lobbyists. "Since they couldn't sell it by logic, they had to roll out all the heavy guns."

Supporters of producing new chemical bombs and artillery shells could still try to prevail in the Senate, where the military procurement bill has not yet reached the floor, and then in conference. But Bethune, whose district adjoins the Pine Bluffs, Ark., arsenal where the nerve gas would be produced, said, "I think the members will probably tell them they don't want to have another debate on nerve gas this year."

The chemical weapons debate came as the House considered a $188 billion weapons procurement bill, which the Armed Services Committee scaled down from Reagan's original request of $199 billion. The most controversial portion of the bill, a request for funds to begin building MX missiles, is scheduled to be considered after the July 4 recess.

Other attempts to reduce the record procurement request were defeated easily on the House floor yesterday, following similar victories Tuesday for the administration and the committee. A proposal by Rep. Ronald V. Dellums (D-Calif.) to delete funding for the controversial B1 bomber failed by a 255-to-164 vote, almost as decisive as Dellums' 257-to-142 defeat on the same issue last year.

An effort to cut some funds for the division air defense gun, also known as the Sergeant York, was defeated, 283 to 134.

Most of the day's debate, more than three hours, was devoted to the chemical warfare issue, and for a few minutes it seemed the House would reverse last year's position. When time ran out on the vote clock on the crucial amendment, proponents of chemical production were leading by 10 votes. But last-minute Democratic arrivals and vote-switchers tipped the balance.

Rep. Marvin Leath (D-Tex.), a member of the Armed Services Committee, led the fight for a resumption of nerve gas production, saying that only such an action would convince the Soviets to abandon the chemical weapons which administration officials say have been used in Afghanistan and Southeast Asia.

"There is no question that chemical weapons are horrible," Leath said. "But real arms control is the issue . . . . During World War II, the reason the Germans or the Japanese did not use chemical weapons was they knew there would be an immediate retaliatory force."

Leath said that during the 14-year self-imposed U.S. moratorium on nerve gas production the Soviet Union has built "a truly impressive arsenal" while stalling negotiations. He said American opposition to chemical weapons impedes progress for the U.S. representative to the Committee on Disarmament in Geneva.

"The public debate on binary new chemical weapons has the effect of reducing such leverage he may have and of damaging the negotiations," Leath said.

But critics said it was the Americans who decided to break off bilateral negotiations on the issue, leaving only the committee's multilateral talks ongoing. Rep. Jim Leach (R-Iowa) also said the United States has engaged in "unilateral restraint," not unilateral disarmament, and still maintains enough nerve gas theoretically to kill all life on Earth.

Leach acknowledged that the absence of chemical weapons for retaliation could make the use of nuclear weapons more likely in some situations. But he said chemical weapons are themselves "mass destruction" arms that could lead to the use of the even more terrible biological weapons.

Leach was among the few who discussed the moral aspects of chemical weapons. Bethune said this was partly intentional.

"We are frequently accused of using emotionalism," Bethune said. "I think it's plain we stuck to the facts; we didn't need to resort to emotionalism." Then he added with a laugh: "Maybe next year."