The Department of Energy told Congress earlier this week that it has taken a new step toward building neutron weapons, the new generation of short-range, nuclear warheads and artillery shells that has caused a political uproar in the North Atlantic Treaty Organization for four years.

The department was acting in response to a little-notice section of the nuclear weapons authorization bill, according to congressional sources, and not in response to a specific presidential decision to go ahead with the controversial enhanced-radiation weapons.

President Carter deferred production of the new weapons in 1978, choosing instead to build low-yield nuclear versions plus the components that could be inserted into them to make them neutron. A basic ingredient in the components was to be the radioactive material tritium.

The Carter administration then decided last year not to allocate the tritium to complete the components because tritium, which is used in making hydrogen bombs, was needed for larger nuclear weapons.

Last Monday, the Department of Energy told the House Armed Services Committee that production has begun on a new Lance missile nuclear warhead, which was to be the first neutron weapon produced, and that tritium needed for insertion components had been allocated to the weapons program.

The committee, according to Capitol Hill sources, was also informed that initial production of the new eight-inch nuclear artillery shell, planned as the second neutron weapon, and its components and necessary allocation of nuclear material would begin next month.

The Energy Department, according to congressional sources, "is only obeying the law," a reference to the section of the law passed Dec. 17 after President Reagan was elected. In that section, Congress directed the energy secretary to build all of the parts for neutron weapons and set aside necessary nuclear materials.

A top official at the Pentagon said the Energy Department acted even though the White House has not made a final decision on whether it will mate the two portions of the weapon or keep them separate. A review is under way and will weigh the international implications of any action.

The Reagan administration has had problems with NATO allies over neutron weapons. The difficulties were sparked last January when Defense Secretary Caspar W. Weinberger told his first news conference that he favored production and deployment to Europe of the weapons.

Secretary of State Alexander M. Haig Jr. had to inform the allies that Weinberger's statement did not represent administration policy and that no action would be taken on the neutron weapons until there had been thorough consultation among the North Atlantic alliance members.

Given current political difficulties over deploying long-range missiles in Europe, introduction of the neutron weapons could only make that situation worse, an administration official said Wednesday.

Before Reagan's inauguration, his transition team suggested that the low-yield weapons be produced and sent to Europe while the components and material to make them neutron weapons be stored in the United States until they might be needed.

But a top Defense Department official cautioned that the White House understood that even building the components represent a "serious policy decision, and that hasn't been made."

Political opposition to neutron weapons runs particularly high in Europe, primarily because they are designed to be used on Western European territory. p

Neutron weapons primarily produce radiation as their kill mechanism, rather than blast and heat as is the case with nuclear weapons now deployed with NATO forces. That charisteric, supporters of the weapons argue, makes them more useful in battle since they cause less damage to nearby towns and cities.