An official of the Arms Control and Disarmament Agency, decrying the nuclear freeze movement as an "immoral" campaign inspired by the Soviet Union, came here today to help defeat a freeze resolution that had sailed through the Virginia House of Delegates with virtually no dissent.

The testimony by the Reagan administration official capped a spirited legislative debate over the nuclear arms race that included pleas for the resolution by the Catholic bishop of Richmond and some behind-the-scenes lobbying against it by executives of the state's largest private employer, Newport News Shipbuilding and Dry Dock Co.

By the time the furor had subsided opponents were denouncing the resolution as a threat to U.S. security and the resolution's chief sponsor, Del. Bernard S. Cohen (D-Alexandria), angrily was blaming "kooks in the Defense Department" for its defeat. Although the measure had cleared the 100-member House with barely a murmur of dissent, it died in the Senate Rules Committee today by a vote of 10 to 3.

"I think it's absolutely incredible that the Reagan administration would have somebody come down on a resolution like this that has no binding effect, that's merely a sense of the General Assembly," Cohen said.

The star witness against the resolution, and the object of Cohen's wrath, was Bernard F. Halloran, a special assistant to the Arms Control Agency's director and a former military analyst with the Army Chief of Staff. He arrived with an eight-page statement and supporting documents that included charts comparing U.S. and Soviet intercontinmental ballistic missile and submarine strength.

"I feel it would be a horrible shame if the representatives of the people of the State of Virginia were to endorse in any way a proposal put forth by the Soviet Union which jeopardizes so severely the safety of the people of the United States," said Halloran. "I would beg you to preserve the honor of Virginia and defeat this sadly misguided effort."

Halloran's testimony drew protests from Catholic Bishop Walter Sullivan of Richmond.

"I really object when somebody says this is a Moscow-inspired effort to weaken the U.S.," Sullivan told the committee. "The spread of nuclear weapons is going on and on and on and there's nothing to stop it, nothing on God's green earth."

In response to a question from Sen. Adelard L. Brault (D-Fairfax), Halloran said that he was speaking for himself and not for the administration. Halloran said later, however, that the State Department had received requests from freeze opponents for a speaker to testify against the resolution.

"The call was passed to me when there was nobody in the State Department who was a resident of Virginia and was qualified to speak," Halloran said. "I asked my boss, and he said, 'Sure.' "

State Department spokesman Joe Reap said today that the administration believes that a nuclear arms freeze would perpetuate "an imbalance" in military forces and added: "We're trying to do better than a freeze. We're trying to get reductions." He said that it was not administration policy to attempt to defeat freeze resolutions that are proposed at the state and local level.

Eleven state legislatures and 382 city and county councils have passed resolutions urging a nuclear weapons freeze, according to a group in St. Louis called the Nuclear Weapons Freeze Campaign. Although Cohen's resolution was not drafted in conjunction with the freeze groups, it had the same basic purpose.

It would have called upon the president and Congress to initiate negotiations for a "verifiable reduction and morotorium on deployment of nuclear weapons with the Soviet Union," and transfer funds from nuclear weapons to "the domestic betterment of the American way of life."

During the past week, several senators said, they had been deluged with telephone calls and with visitors concerned over the resolution, including some from executives of Newport News Shipbuilding, where the nation's nuclear aircraft carriers are built.

"Do you think for one minute the Russians will pay any attention to what we say?" said Senate Minority Leader William A. Truban (R-Shenandoah). "They don't even pay any attention to what America says."