The White House cited Soviet deployment of a new 75-mile range nuclear-armed missile yesterday as grounds for congressional support of President Carter's defense budget proposals as well as a new arms limitation agreement with Moscow.

Presidential press secretary Jody Powell told reporters in a carefully deliberated statement that deployment of the missile in East Germany will be one of the factors considered by Carter in deciding whether to deploy so-called enhanced-radiation, or neutron, weapons with NATO forces stationed in Western Europe.

Powell was responding to a report in yesterday's New York Times that the Soviet Union has begun to deploy a new tactical nuclear missile, known as the SS21, in East Germany. The missile, one of three new tactical nuclear weapons the Soviets recently have developed, is really more of an artillery shell. It is similiar to the American Lance missile, deployed with NATO forces in Western Europe in 1972.

In response to a question, Powell denied a suggestion that the administration may have deliberately made deployment of the Soviet weapon public at this time to affect congressional budget or other deliberations. But he nonetheless seized on the report to argue for support of the president's defense budget proposals and for Senate approval of a new strategic arms limitation treaty (SALT), which is expected to be signed soon.

Powell said the deployment of the SS21 "was not a surprise" to the administration, which he said has long been aware of Soviet efforts to modernize its tactical nuclear forces in Eastern Europe. He said awareness of this Soviet modernization program was one reason Carter, in his budget proposals for the fiscal year that begins Oct. 1, called for a 3 percent increase in spending above the rate of inflation for NATO forces.

Powell praised Congress' handling of the fiscal 1980 budget request, but said the administration is concerned about a supplemental defense spending request for the current fiscal year. He suggested the new Soviet weapon should be taken into consideration in the congressional debates.

The administration has asked Congress for $4.4 billion in supplemental defense spending for the current fiscal year. An Office of Management and Budget official said the chief problem for the administration is a resolution by the House Budget Committee that would effectively eliminate about $2.1 billion in the supplemental request.

The official said the $2.1 billion includes funding for a number of NATO-related items, including money for development of an antitank program and funds for the Army's Pershing II land missile.

Missiles such as the SS21 and the Lance are "tactical" nuclear weapons and are not covered by the current SALT II negotiations. But Powell argued yesterday that these shorter-range nuclear weapons will never be limited in a subsequent SALT III treaty unless the Senate approves the SALT II accord.

"The successful negotiation and ratification of a SALT II treaty is essential to permit us to go on to SALT III," Powell said.

The press secretary also said that Soviet modernization of its tactical nuclear weapons "will be a part" of Carter's deliberations on deployment of neutron weapons. Last year the president ordered a modernization of U.S. weapons in Europe to allow use of the neutron warheads, but delayed a decision on their actual deployment.