The violent events of recent days in Lebanon and Grenada are being used by President Reagan to present a bold but risky and ambiguous policy meant to warn Moscow and its allies that a resurgent America will respond, perhaps militarily, to provocations wherever U.S. interests are perceived to be threatened.

The potential gain for the administration in such a policy is to send a strong signal--especially to a number of smaller countries such as Cuba, Nicaragua, Libya and Syria--of American preparedness to act that may give them pause about continuing to support guerrilla warfare elsewhere or undertaking new actions.

But the risk and the ambiguity lie in the administration's apparent determination to tie the Soviet Union publicly to all the violence around the world that the president and his aides have been talking about in recent days.

For example, in his address to the nation last night, the president described the recent terrorist bombing of the Marine headquarters in Beirut and the need for the United States to invadeGrenada as "closely related" events. "Not only has Moscow assisted and encouraged the violence in both countries, but it provides direct support through a network of surrogates and terrorists," Reagan said.

Similarly, three times in the last two days a top administration official who briefed different groups of reporters on condition that he not be identified did so in a way that clearly implied to his audience that Moscow was behind the recent violence everywhere, from Burma, where a terrorist bomb killed several South Korean government officials this month, to Beirut.

This implication was so strong that in all cases, the first question he got from reporters was whether he was claiming that the Soviets were behind the Beirut bombing of the Marine headquarters. The official quickly said: "No, absolutely not" and added that he did not think the Soviets "would have allowed it to happen" had they known about it in advance.

What seems to be happening is that the administration is more careful about what it says about Moscow in private than what it says in public.

On the one hand, the administration is genuinely convinced that the Soviets are behind many events around the world. But beyond this, Reagan and his aides also seem to feel that they can better explain their actions and mobilize more public support by laying events at the Soviets' door.

The danger in this is that imprecision can heat up the already bitter rhetoric between the two superpowers, drive relations to an even lower point and perhaps lead to consequences neither country wants.

The administration is trying to get across a rather sophisticated message that includes some seeming contradictions. Yet it is trying to explain it publicly in terms that are very black-and-white.

The message is this, as laid out by the senior official:

"The Soviet Union is a very cautious power" that does not seek a confrontation with the United States. But in the past decade, as Moscow has achieved at least parity and possibly some edge over this country in atomic striking power, the Soviets have grown bolder in moving against American interests through use of surrogates such as Cuba in Central America, Angola and Libya in Central Africa and East Germany in Ethiopia.

Now, the official says, the West is facing more varied and unpredictable Soviet probes around the world, still through surrogates but also with a terrorist dimension, with which democracies, in particular, have trouble dealing.

Whatever the degree of validity to this, it is hard for the administration to make its case through the media and develop public support for a bolder military response without tying the Soviets closely to every event. Thus, the official and the president last night cited recent events in Beirut and Grenada as two of these "probes" of American interest that now make up Soviet strategy.

Similarly, whatever the reasons for invading Grenada, the act itself quickly has become a symbol of a new American strategy that the administration hopes will deter any more Soviet probing.

The message to the Soviets and their allies is that the United States is capable of taking what might have been considered surprising and unpopular military action only a short time ago.

This is not a new idea. President Nixon used it in the early 1970s when he bombed the North Vietnamese capital of Hanoi on Christmas Day and mined the harbor of Haiphong while Soviet ships were in it, and alerted U.S. nuclear forces during the 1973 Arab-Israeli war.

The invasion of a tiny island in the Caribbean might seem to have a comic-opera quality to it in comparison with those earlier acts. And the United States has drawn reproofs from many of its allies around the world for the invasion.

But administration officials believe that the swift, well-executed attack may have a sobering effect in Cuba and Nicaragua, for example, and may introduce a new element into Soviet thinking.

The idea, Reagan said last night, is "to deter by a record of demonstrating that this terrorism will not be allowed to succeed."

But to be able to deter such a probing strategy requires a different kind of military force than the one Americans have become accustomed to. Rather than images of standing armies defending against a mass attack by Soviet forces across Europe, the more realistic threat lies in odd places with names few people have heard of.

Flexibility is required, with quick-reaction forces, easy to move, and lots of ships, planes and aircraft carriers. Those make up a big chunk of the Reagan defense budget. If, when the dust settles on the Grenada invasion, the president is judged at home to have acted wisely, it may well make it easier to get money for such forces in Congress.

But it also may make it easier to decide to do it again somewhere else. The senior officials emphasize that the United States is not adopting a policy of confrontation and prefers to negotiate rather than fight. The challenge will be to manage a policy Reagan describes as "a willingness to respond to violence firmly" with precision of language and charges and without it spinning out of control.