The White House has delayed for two months a go-ahead on production of Lance missile nuclear warheads and 8-inch shells because of an internal administration dispute over a plan to convert them quickly into neutron weapons.

Last April 7 President Carter side-stepped the controversial neutron weapon issue by announcing he would defer their production to see if the Soviets would make a reciprocal arms control gesture. At the same time he ordered a "modernization" of the Lance warhead and the 8-inch shell.

A significant ommission in the president's announcement and his orders to the Pentagon to implement them was that "modernization" meant building the same new nuclear warheads and shells as originally planned in the neutron program but leaving out the core elements which transform them from a conventional nuclear waapon into a neutron weapon.

These core elements lower the blast and hear effects of the conventional nuclear weapon and enhance its output of radiation.

Administration sources said yesterday that the neutron components once built can easily - with some technical work - be inserted in the new Lance warheads and 8-inch shells to make them neutron weapons long after the warheads and shells had been deployed to Europe.

According to White House press secretary Jody Powell, who released Carter's April 7 statement, "it was classified how easy it was to do" to convert the "modernized" conventional nuclear weapons into neutron weapons.

According to Department of Energy officials, a presidential go-ahead on the "modernization" program had been expected before the end of April.

The delay in the production go-ahead, according to informed sources, stems from bureaucratic arguments in the administration on whether to proceed with a two-step program or build both the nuclear weapons and the neutron core elements at the same time.

According to White House sources, the president's original intent was to go ahead with the nuclear weapons and wait 18 months before proceeding with the neutron core elements.

In that time, the Soviets would have an opportunity to make some response which, if deemed appropriate, would further delay or eliminate production of the neutron cores.

Outside the White House, however, pressure from neutron weapon supporters on Capitol Hill has pushed Defense and Energy Department officials to press for production of the shells and warheads along with neutron components. The latter would be stockpled in the United States when the weapons are sent to NATO forces in Europe.

The debate, one military man said, is about "the readiness time, the days, months or years after a decision is made before (neutron) warheads are in the hands of the troops."

The Senate Armed Services Committee, acting in the fiscal 1979 Department of Energy national security programs authorization bill has specifically directed that neutron components be built along with the rest of the parts of the shells and warheads. The committee's report on nuclear weapons is expected to be released today.

That approach, however, has created other problems.

Pentagon lawyers are studying whether building components for the neutron core - even if not fitted inside the weapon - would trigger the Byrd-Baker amendment.

That amendment, passed last July, 1978 DOE money bill by the Senate at the behest of the majority and minority leaders - Sen. Robert C. Byrd (D-W.Va.) and Sen. Howard H. Baker, Jr., (R-Tenn.) - requires the president to inform Congress of a decision to build neutron weapons and his reasons. It also gives Congress 45 days to pass a joint resolution in opposition to such a decision.

There is also concern by some Defense officials that producing the neutron elements could undermine any chance of a Soviet response since the opportunity would exist to rapidly change the Lance warheads and 8-inch shells into neutron weapons at any time in future.

These arguments, however, have little impact on a few key officials in the weapons-building program an congressional supporters of neutron weapons. They do not expect any satisfactory move by the Soviets and are focused primarily on the most efficient way to get neutron weapons deployed.

Defense and DOE officials said yesterday they expected a Defense Department proposal "soon" but could not say how long it would take the White House to act on it.