Mr. Reagan could not have delayed much longer in starting START without raising alarm about his nuclear intentions to a level dangerous to his diplomacy as well as to his political standing. As it is, with his speech yesterday, he has made it possible for a more balanced dialogue to resume. He outlined a proposal fulfilling his longstanding promise to negotiate substantial reductions--hence the change from SALT's L for limitation to START's R for reduction--with the Soviet Union. He suggested that the arms control negotiating process, which halted three years ago in circumstances clouded by his own harsh political attack upon it, start again by the end of June.

Not only had Mr. Reagan faulted the process. He had felt that a fascination with it had kept the United States from arming as it should. Taking office, he allowed arms control to be denigrated and jumped into strategic "modernization." These steps, along with his administration's often heedless manner of nuclear speech, created a crisis of alliance confidence. The president met it, in part, by opening talks with the Soviets on Europe-centered nuclear forces.

Here there was not so much a crisis as a building confrontation, part of it public and made evident by the "freeze" movement and part of it quiet within his administration. One faction has insisted that the United States can drive the Soviet Union out of the arms race. The other faction has argued for a stable balance.

Mr. Reagan's speech yesterday indicated he has accepted the logic of the second school. He seemed to be going that way last November. Mr. Reagan accepts that a negotiation with Moscow is worth pursuing. He is not making his strategic policy gratuitously hostage to ongoing political disputes. With equal ceilings as his goal, he envisages a first phase to reduce by a third the number of ballistic missile warheads--by some measures the United States is ahead. He would push the Soviets to put more of their remaining warheads at sea, where they are less prone to be fired at, and thus to be fired, in a crisis. In a second phase, other strategic elements, including the conservatives' traditional bugaboo, missile throw-weight, would be directly addressed.

An argument has been going on about whether Mr. Reagan would frame proposals with an eye to making START succeed or fail. This speech will likely end the argument--on the right: hard-core Reaganites are already shrieking. Elsewhere, his approach may be received with a tentative respect. We think that's about right. Mr. Reagan appears to be in a learning mode on strategic affairs. No one has ever doubted he is tough. He seems now to be adding an awareness of the need for give and take. He promises to listen to what Moscow has to say. We think Moscow should listen to him.