In the strongest expression yet of the Reagan administration's fear of the nuclear freeze movement, Defense Secretary Caspar W. Weinberger said yesterday that Soviet President Leonid I. Brezhnev's hard-line speech to his armed forces chiefs this week shows why American voters should reject freeze resolutions on ballots in nine states Tuesday.

Weinberger warned at his first general Pentagon news conference in nearly two years that "a nuclear freeze would weaken the deterrent forces we rely on to prevent war" and make it "far more difficult" to negotiate arms reductions with the Soviet Union.

As aides passed out charts showing the Soviet Union with a much more modern nuclear force than that of the United States, Weinberger said that Brezhnev's speech Wednesday underlines "even more specifically than anything we could the reasons for not entering into a freeze."

He said Brezhnev "pledged the Soviet Union to continue the path of an even more intensified quest for military superiority," including "a new technology race."

Weinberger argued that, "This requires us to step up our efforts here in the United States, in Europe and in Japan to counter this campaign."

He added, "It's significant that President Brezhnev said nothing whatever during his talk about arms reduction despite the Soviet campaign for nuclear freezes. This stands in sharp contrast to President Reagan's efforts to bring a halt to the arms race."

Brezhnev said in Moscow that the United States had "raised the intensity of their military preparations to an unprecedented level" under "an aggressive policy which is threatening to push the world into the flames of a nuclear war."

Accusing the United States "of trying to attain military superiority," Brezhnev said "our line is a line for detente and strengthening international security. We shall step up our efforts."

He appeared to demand that Soviet scientists and engineers develop planes, tanks and other weapons far superior to those the Israelis destroyed with American arms in Lebanon. "Competition in military technology has sharply intensified," Brezhnev told his military chiefs, "often acquiring a fundamentally new character.

"A lag in this competition is inadmissable. We expect that our scientists, designers, engineers and technicians will do everything possible to resolve successfully all tasks connected with this."

In a separate reaction to the Brezhnev speech, State Department spokesman John Hughes said, "We see the tone was harsh toward the United States, but there appear to be no new policy departures, and we don't intend to comment in detail on Soviet leadership speeches that repeat standard formulations."

Administration officials said last night that analysts believe it is too early to conclude that Brezhnev was throwing down the gauntlet in a new and faster lap of the arms race.

They added that Weinberger's harsh reaction to the Brezhnev speech should be viewed as a political message, not an adoption of a harder line by Reagan.

Answering questions about the nuclear freeze movement in the United States, Weinberger repeated his past assertions that it and the Reagan administration share the objective of avoiding nuclear war and reducing armaments on both sides.

But "if we froze today," he argued, "as a result of the Soviet deployments and our own inactivity, a significant percentage of our strategic retaliatory forces would remain vulnerable" to modern Soviet missiles and "the Soviet Union would have no incentive to negotiate reductions . . . . "

Responding later to this, Randall Kehler, national coordinator of the Nuclear Weapons Freeze Campaign, said, "If Weinberger is worried about President Brezhnev's call for a Soviet buildup of nuclear weapons, he should realize that the freeze would put a stop to that buildup. It would reduce the risk of nuclear war by stopping first strike weapons which both countries are now building.

"The alternative to a mutual freeze is mutual escalation, and ultimately mutual destruction," Kehler said. "Brezhnev's statement yesterday and Weinberger's response today are frightening evidence of this pattern of escalation."

The Committee on War and Peace of the National Conference of Catholic Bishops released a draft position paper this week calling all forms of nuclear war immoral and recommending "support for immediate, bilateral, verifiable agreements to halt the testing, production and deployment of new strategic systems."

Asked about the bishops' statement, Weinberger said, "We think freezing at this point is something that will increase the danger of war. The moral aspects of it should be examined from that point of view. We also, of course, have in mind that his holiness, the pope, at the United Nations -- a message delivered there for him -- indicated that deterrence is a moral policy."

Asked how the Reagan administration intended to slow down the U.S.-Soviet arms race when the current U.S. buildup has not yet prompted a breakthrough in arms control, Weinberger said, "We slow them down by the only means that any of us have any knowledge that will ever work.

"One is deterrence, and the other is to push just as hard as you can for major arms reductions -- not arms limitation formulae that allow them to expand, which is what's happening now and what has been happening all through the years . . . . Nothing slowed them down during the 20 years period that is just closing.

"Mr. Brezhnev referred a number of times to detente and all of that, but all through detente they did enormous expansion year after year on every type of weapons systems, and they're continuing to do it. So his policy in his speech doesn't announce any new policy. His speech announces a continuation of what they've been doing for 20 years."

Voters in Arizona, California, Massachusetts, Michigan, Montana, New Jersey, North Dakota, Oregon and Rhode Island will decide Tuesday whether to urge Reagan to start talks with the Soviet Union on a mutual freeze of the manufacture and deployment of nuclear weapons.

Resolutions directing mayors to demand a freeze are on the ballot in 30 cities and counties, including the District of Columbia, Chicago, Denver, Miami, Philadelphia and Reno. Weinberger Says U.S. Sending Artillery, Carriers to Lebanon

Secretary of Defense Caspar W. Weinberger confirmed yesterday that the Reagan administration is sending artillery and armored personnel carriers to Lebanon to help rebuild the Lebanese armed forces.

"We'll continue that flow" of military equipment to Lebanon, he added, "to the extent that Congress will permit us to do so, and I hope they will. It's a very important priority."

In discussing Lebanon at his Pentagon news conference, Weinberger said, "My views are that it is very necessary for us to do everything we can to strengthen the Lebanese government and help them strengthen Lebanese armed forces so that they can maintain security and the sovereignty and the sanctity of their borders, and not allow their country to be used as a platform for any shelling or bombing of any other country, or to be used as a maneuver ground for foreign forces."