The surprise presence of Richard V. Allen, President Reagan's national security assistant, at an unpublicized meeting in Defense Secretary Caspar Weinberger's office Jan. 30 conveyed the unspoken message that Reagan's personal prestige is deeply committed to higher defense spending.

Participants in the closed-session, held at the unheard of hour of 7 o'clock that Friday evening, were Weinberger, Deputy Secretary Frank Carlucci, David Stockman, director of the Office of Management and Budget, Stockman's defense aide, William Schneider, and Allen.

Allen arrived 20 minutes late, but his presence sent unmistakable word to those two novitiates of military matters, Weinberger and Carlucci. The message: Reagan's plan to boost defense spending almost 10 percent for the next five years is essential not only to rebuild American strength but to inform U.S. allies that after 10 years of retreat, the corner has been turned.

"Reagan wants Giscard and Schmidt to know his election was not an aberration but a profound change," a top aide told us. "This five-year defense plan proves it. It will set the course of the West for the next 20 years."

This optimistic conclusion could prove premature, but it explains the elaborate preparations inside the White House to make certain that Weinberger and Carlucci would make no effort to scuttle the preparedness budget crafted by Stockman, Schneider and the non-political technicians inside the OMB.

The strategy worked. Aside from a whispered remark by Carlucci that the new five-year plan, which adds $200 billion to the spending projected by President Carter, is "one hell of a lot of money," the Stockman-White House proposal was approved. Details on precise numbers and types of new weapons remain to be worked out. But the concept of a 9 percent real defense growth over the five-year period was not seriously disputed.

If Congress buys most of this increase in what Reagan calls the "refurbishing" of depleted U.S. military power, a resource base for weapons' procurement will be put in place that simply does not exist today. Unlike some of the defense games played during the early-Nixon years, this resource base is not designed by Reagan men for bargaining-chip diplomacy with the Kremlin. It aims at fast production of real weapons.

How strongly dedicated the neophyte defense team of Weinberger ("Cap the Knife" in a previous incarnation as Richard Nixon's budget director) and Carlucci is to this concept is still not wholly clear. But the Pentagon's new overlords do not understand Reagan's personal commitment. Moreover, defense transition chief William van Cleave, even though discarded, is still having an impact. He could hurl damaging verbal warheads at Weinberger from the Republican right in the event of attempts from his office to undermine the 9 percent growth budget.

To Reagan, Allen and Secretary of State Alexander Haig, the substantial Reagan increase in the Carter budget is essential to put flesh on the bare bones of Reagan's new, activist foreign policy. An example is the private talks now starting between the United States and France to block Libya's Col. Muammar Qaddafi from expanding his new power base in central Africa, possibly from Chad toward Sudan -- a state now anchored to the West. French President Giscard, skeptical about the Reagan mandate, talks cooperation with Washington but acts with caution, uncertain of where the United States is really going.

The unprecedented peacetime buildup of America's defenses should ease that caution, a psychological gain fully as important to Western security as the actual military gain from more and better weaponry.

The size and scope of the Reagan defense program will also help West German Chancellor Schmidt force the issue of the neutron warhead with his appeasement-minded left wing. Haig's reluctance to second Weinberger's quick approval of the neutron weapon was in deference to Western European sensibilities, not a veto. So long as American strength was visibly declining in comparison with the Soviet Union, taling tough in Europe was a high-risk, no-win gesture even for Schmidt.

But the promise of Reagan's new defense program, if pushed through Congress by Weinberger and Carlucci, gives Schmidt a counterweight against the smooth left-wing politicians who claim the United States can no longer act the part of a genuine superpower.

Reagan has signed a contract with the future that destroys such damaging counsels.