Defense Secretary Caspar W. Weinberger said yesterday that in a crisis, neutron weapons stockpiled in the United States could be delivered to troops in Western Europe within "only a few hours" after approval for their deployment is obtained from NATO allies.

Thus, he told reporters yesterday, "there is no penalty" in keeping the new, controversial nuclear weapons in the United States instead of deploying them to Europe in advance.

By leaving them in this country, he added, the United States can avoid "inconclusive debates with allies" about whether the missiles and artillery shells would be accepted on the allies' soil.

Weinberger's news conference late yesterday afternoon was one of a whirlwind of appearances, including seven television interviews, in which he defended President Reagan's decision last week to produce neutron Lance missile warheads and eight-inch artillery shells.

Weinberger advanced several specific ideas during almost every session. These included:

Possession of neutron weapons would serve as a deterrent in itself and make less likely a Soviet invasion of Western Europe.

"I think the fact that the weapon is there means that it's much more likely that this kind of an attack will not come," he told one television interviewer.

The decision to proceed with neutron weapons production will aid arms reduction talks because the United States must approach the Soviets with "as much strength as possible."

"I think we will enter those negotiations whenever they take place, on whatever subject, a great deal stronger and with a far more effective defense," Weinberger said.

Opposition to deployment of neutron weapons in Europe is "largely a tribute to the effectiveness of the Soviet propaganda campaign against this weapon."

The administration made its production decision without waiting for approval from NATO countries where neutron weapons would be deployed and used because it wanted to avoid the "record of vacillation" that marked the way in which former president Carter handled the situation.

Carter supported production of neutron weapons but reversed himself in 1978 when he could not get support for their production from NATO. Instead, Carter ordered most but not all components of the weapons produced but not assembled as weapons.

The Carter approach, Weinberger said, "gave the impression of a weak, irresolute America," an image that Reagan wanted to avoid.

Several times during the day, Weinberger seemed to be saying that the administration was forced into making the production decision by a "mandate of the Congress."

The fiscal 1981 defense authorization bill directed the president to produce and stockpile all components of the neutron weapons but not to assemble them as usable. Under questioning, Weinberger said he had interpreted that language to mean they had to be assembled.

Weinberger said the new neutron weapons would not replace the need for additional conventional weapons in the face of Soviet and Warsaw Pact forces in Europe. But they "did help to quickly balance" the armor and manpower advantages attributed to potential enemy forces, he said.

Weinberger refused to answer a question on whether production of new eight-inch neutron shells would permit the United States to retire the 20-year-old nuclear shells now based in Europe. Instead, he said, he could not discuss the specifics of nuclear weapon deployments.

One public justification given Congress for building the new shells is the need to replace aging ones whose yields are so large that they would cause enormous collateral damage to West European villages and whose range is only nine miles.

The advantage of neutron weapons is that their main destructive power is radiation, rather than heat and blast. They can be used more easily against Soviet tanks, penetrating their armor and killing their crews, rather than blowing them up in a barrage that would destroy towns in the vicinity of battlefields.