Development of a long-range European-theater mobile ballistic missile system for use by the United States and its NATO allies has been authorized by House and Senate conferees in the fiscal 1979 defense authorization bill.

Currently, the Pershing, "with a stated range of 400 miles, has the longest range of any missile in the NATO arsenal.

Deployed with U.S. and West German forces the Pershing could not reach Soviet soil.

The missile system envisioned by the conferees would have a much greater range and would be able to hit targets in the Soviet Union. The conferees' report will be released today.

In the late 1950s and the 1960s, Pentagon efforts to develop similar missile systems were halted because, as one former Defense Department official put it yesterday, "our diplomats did not want something on the (European) continent hat could strike the Soviet homeland."

Now, however, congressional sources say the proposed new system is being pushed to counter the new Soviet intermediate-range SS20 mobile missile. Deployed in western Russia, the SS20 is aimed at NATO targets more than 1,000 miles away.

President Carter and other western leaders have criticized the SS20 calling it an example of Soviet escalation of arms in the European theater.

The manner in which the House-Senate conferees proposed that the new missile program be financed may resurrect interservice rivalries that existed over control of missile systems.

The conferees took $10.1 million from the Army's research and development account - money requested to continue development of a new Pershing II - and gave it to the Air Force with an additional $99 million.

That $20 million the conferees said, was to be used for continued development of the Pershing II reentry vehicle "and to initiate a $2 million design effort for a long-range mobile ballistic nuclear missile."

Yesterday, neither the White House nor the Defense Department would comment on the conferees' action.

One administration source said an interagency study of theater nuclear weapons is under way and would lead to a presidential decision this fall on what weapons should be developed.

"It looks like Congress is trying to get into this policymaking operation before it is finished," one administration officail said.

The Pershing has always had some controversy surrounding it, particularly its range.

Its currently stated range, 400 miles, was first established under an interservice agreement reached in the 1950s when the Army was taken out of the long-range missile game.

Army missilemen, however, were reportedly not deterred by that decision, a former officer said recently. He and other Army officers said privately that the Pershing now deployed in Europe could probably be fired more than 700 miles.

With reported yield ranging from 60 kilotons to more than 375 kilotons, it is supposed to be aimed at Warsaw Pact airbases and other military targets.

Many of the 180 Pershing launchers in Europe are on 15-minute alert.

The Pershing II has been under way for four years and is said to have a particularly accurate reentry vehicle.

When the missile gets to within a certain altitude above the target the nose cone radar matches what it picks up from the ground with a prestored reference map of the area.

It then automatically corrects itself to give it increased accuracy.