The Reagan administration has mobilized its defense and foreign affairs specialists to draft a major policy speech on arms control for possible delivery by the president later this month, government officials said yesterday.

They said the objective is to assure people in the United States and abroad that President Reagan is vigorously pursuing ways to reduce nuclear arsenals and lessen the chance of accidental war.

Although the speech drafts were ordered before the election, the strong showing made by nuclear freeze resolutions at the polls on Tuesday gave added impetus to the effort, officials said.

The ideas discussed in drafts circulating at the Pentagon and State Department include seeking agreement with the Soviet Union to shift emphasis from nuclear to conventional arms programs, and each nation notifying the other before starting menacing training exercises. Stress is being placed on "confidence-building" measures to minimize the chance that either nation would fire nuclear weapons in response to false alarms.

But one civilian official in the Pentagon, who said he submitted a draft for the possible presidential speech, said it would be "hare-brained" to suggest Reagan might undercut the U.S. nuclear arms-reduction proposal now on the table at negotiations with the Soviets in Geneva by proposing a mutual shift of defense resources to conventional arms.

Other confidence-building measures more likely to pass muster as the speech drafts move through the bureaucracy include some that Reagan has already promised to present to the Soviets. Reagan announced in Berlin in June that "we shortly will approach the Soviet Union with proposals in such areas as a notification of strategic exercises, of missile launches and expanded exchange of strategic forces data."

Edward L. Rowny, who is Reagan's chief nuclear arms-control negotiator, disclosed in September that those confidence-building proposals had never actually been proposed by the U.S. at the Geneva talks. Their inclusion in a forthcoming presidential speech would not represent anything new, but officials said it could serve as a gesture of Reagan's seriousness about arms control.

Pentagon civilians and the Joint Chiefs of Staff want the president to stress that deploying enough nuclear weapons to match the Soviets would deter rather than trigger nuclear war. State Department officials look for stress on the president's commitment to arms control. The U.S. Information Agency analyzes how the drafts would play before the world audience.

The drafts have not yet been reviewed by top administration officials. In the end, the president may decide against giving any speech at all, officials cautioned.