Principles of foreign policy. Keys to stronger defense. A strong suspicion of the Soviet Union and the need for preeminent US military strength are two unifying principles of the political right.

WHEN hundreds of conservative activists met here recently for their annual convention, there was one battle cry that always brought cheers and applause: ``SDI -- now!''

The Strategic Defense Initiative, often called ``Star Wars,'' has become the cutting edge of conservative military policy.

Sunday, Mar. 23, will mark the third anniversary of President Reagan's call for this multibillion-dollar program that he says eventually could render nuclear missiles ``impotent and obsolete.''

Yet when it comes to SDI, many gung-ho conservatives have one-upped even their own Republican President.

Mr. Reagan wants to find out by the mid-1990s whether a defensive system could be deployed against Soviet intercontinental ballistic missiles.

Conservatives in Reagan's own party don't think that's good enough. They want SDI now.

Sen. Malcolm Wallop (R) of Wyoming has been an SDI booster for years, and he is surprised and disappointed that the President hasn't moved more quickly toward strategic defense.

``The fundamental complaint that I've had with the Reagan administration is they say they're engaged in a study to determine whether it's possible [to build SDI]. And they know that it is,'' says Senator Wallop. ``We have put ourselves into the situation where we are studying things we know how to do.''

Wallop served for eight years on the Senate Select Committee on Intelligence. He has become a point man for conservatives worried that the President has failed to follow through on his tough rhetoric on foreign and defense policy.

A major complaint of the right is that the Reagan White House has made SDI seem like some great mystery, something almost as fantastic and futuristic as intergalactic travel. Says Wallop:``The Reagan administration has been perpetuating a myth that this is somehow or another a mystical achievement. And it is not a mystical achievement.''

Equally frustrating to the senator, who was interviewed at his Capitol Hill office, has been the public impression that Reagan has pushed ahead rapidly with SDI research. Wallop complains: ``There isn't anything that's in SDI [research] today . . . that wasn't started in the Carter administration or before. There's nothing new in it.''

In fact, work on some key elements of the program has actually been reduced since the Carter Administration, says Wallop.

Conservatives argue that foot-dragging on SDI is inexcusable on Reagan's part because of rapid improvement in Soviet nuclear capabilities.

Sen. James A. McClure (R) of Idaho, chairman of a subcommittee that oversees the US nuclear warhead program, recently told his colleagues that the Soviets are steadily widening their lead over the United States.

Today, the Soviets hold a 3-to-1 lead (6,400 Soviet intercontinental warheads to 2,100 for the US). By 1991, the Soviets are expected to have 10,000 to 13,000 ICBM warheads, while the US will have only 2,800, Senator McClure says.

Senator Wallop says this trend is accompanied by two developments that are increasing US vulnerability.

First, Soviet missile accuracy and killing power are steadily increasing. The Soviet's ability to destroy US land-based missiles, submarines in port, and the American bomber force are growing to dangerous levels. The potential effectiveness of a Soviet first-strike increases every year.

Second, the Soviets are nearing deployment of new, land-based strategic strike weapons, the SS-24 and SS-25 missiles. These missiles, the first of which will be put into the field this year, will be mobile. With mobility, they will be extremely difficult to attack.

Says Wallop: ``By the early 1990s, just about all the warheads that the Soviets do not plan to use in a first strike will be mobile in some way. We won't be able to find them. If we do, we almost surely will find them defended by mobile antiballistic missile systems.''

The Soviets, warns Wallop, are ``now more than one generation ahead of us in weaponry.''

The senator says all of these factors are moving the Soviets toward what is called ``breakout.'' That is, the Soviets would have the ability to strike the US suddenly, wipe out most of this country's land-based missile force, and be reasonably sure that even a full-fledged US counterstrike could not destroy remaining Soviet missiles.

``Their posture for breakout is increasingly imminent,'' says Wallop. ``[If] unresponded to by the United States, my feeling is that they could achieve it within a decade.''

Conservatives are concerned that after a full-fledged Soviet first strike the US would have left only weapons capable of striking Soviet cities -- an option which they consider impractical.

They are particularly frustrated because the Reagan White House is spending billions of dollars for strategic weapons, yet is failing to address these two major weakness in US strategic policy.

Even with new weapons, such as the B-1 bomber and the MX missile, we have failed to ``protect our forces and threaten theirs,'' says Wallop. ``That is the essence of deterrence,'' he says. ``It is also the essence of survival.''

He continues: ``I do not mean to say to you that the 50 MX missiles that this administration has programmed, or the 100 B-1 bombers, or the 600-ship Navy, or the sea-launched cruise missiles and perhaps a Stealth bomber fleet are nothing. In absolute terms they are impressive, though not so impressive as their cost.

``But in the real world, weapons must be judged in relation to their tasks -- and to the enemy's weapons and strategy. And in these terms, I fear that our costly buildup amounts only to more expensive things . . . for the Soviets to kill.''

At another point, Wallop describes Reagan's strategic buildup as ``of little consequence and very expensive. It does not do anything about addressing the growing imbalance between us.''

The US ``won't and shouldn't'' strike first, Wallop notes. That means America must find some way to defend itself even if another nation hurls 6,000 warheads toward it.

Conservatives such as retired Gen. Daniel Graham, director of High Frontier (a private, nonprofit foundation which promotes SDI), have argued that the only practical answer for the US is the Strategic Defense Initiative.

The great deception being practiced by critics of SDI, says General Graham, is that the defensive system must be ``perfect'' to be effective. This requirement for an impenetrable missile shield is nonsense, he argues.

Wallop echoes that point. If a defensive system were even 5 percent effective, the senator says, it would require the Soviets to increase their throwweight by 37 percent to have equal assurance of destroying US targets.

How quickly could SDI be working?

``Within five years we could have an effective point defense of some missile systems and some cities,'' says Wallop. ``Within a decade there is no doubt in my mind that we could have a boost phase defense of some capability.''

Conservatives argue that the United States, through inaction, is allowing the Soviets to threaten this country unnecessarily. The US, they say, has the ability to provide itself with a credible strategic defensive system.

Says Wallop: ``Let me be very clear. They are not ahead of us in technology. But technology is only important to the extent that it is used.''

Dr. Edward Luttwak, a senior fellow at the Georgetown Center for Stategic and International Studies, notes that the US has ``wealth and we have technology.''

What this country sometimes lacks, he warns, is the necessary will to use them.