The oldest man ever to deliver a State of the Union address resembled the lad about whom Longfellow wrote so stirringly. You remember: The shades of night were falling fast as through an Alpine village passed a youth who bore 'mid snow and ice a banner with the strange device "Excelsior!" The boy meant: stay the course.

Reagan's speech was almost undiluted Reaganism: rapid rearmament, restrained domestic spending. The slight dilution was a gingerly acceptance--on certain conditions--of a contingency tax. This implies acceptance of the fact that the government's revenue base must be restored.

The president's new passion, "bipartisanship," is, like Jesus's injunction to love your neighbor, more frequently praised than practiced. Unlike Jesus's injunction, bipartisanship may be a lousy idea. The president's model of bipartisanship is the Social Security reform commission, which means giving the hard questions to Alan Greenspan to settle. Anyway, someone is "partisan" when he has a passion you disapprove. I am principled; you are partisan.

Because Reagan has spoken for so many years on behalf of a few clear convictions, it is hard for him to avoid sounding like an echo of an echo. However, he did not come before Congress as the boy who stood on the burning deck whence all but he had fled--The Last Supply Sider.

The only applause that was more than perfunctory was for this: "We who are in government must take the lead in restoring the economy." That sentence is a jug into which any wine of meaning can be poured. But it may be a milestone in conservatism's long march to maturity, because it appeared in a speech blessedly free of Reagan's usual anti-government rhetoric. Perhaps word has seeped through to his speechwriters that Reagan is the government and that, like all presidents, he will be held responsible for aggregate economic performance.

For 30 years, Reagan has deplored the centrality of government in our lives; especially the centrality of the central government; not least the central role of the president in the central government. Yet his task today is to use his office for the ambitious and delicate task of altering behavior by manipulating mood.

He accepts this analysis of current discontents: lower interest rates are the key to recovery. The price of money contains a fear component--a premium expressing fear of future inflation fueled by gargantuan deficits even after recovery begins. Hence the freeze (details to come) on domestic spending, and a tax increase to be triggered if the fiscal 1986 deficit is projected to exceed 2.5 percent of GNP.

Reagan believes the economic tinder is dry and ready to blaze. The number of persons in the family-forming (25 to 35) years means pent-up demand for houses and appliances. That group, which generally spends an exceptioally high percentage of its discretionary income, has an unusually large amount to spend: its installment debt is down and its savings are up. Reduced inflation has strengthened the purchasing power of Americans; July brings another tax cut.

A single-digit prime interest rate would be psychologically transforming. Single-digit car loans would set assembly lines racing. The average age of the 123 million cars on the road is seven years, up from about four years in a decade. There are 15,000 parts in a Chrysler. Quicken sales and you will pull people back to work making steel (Bethlehem, Pa.), glass (Pittsburgh), tires (Akron, Ohio, and Lawton, Okla.), windshield wipers (Buffalo), radios (Huntsville, Ala.), wiring (Black Mountain, Tenn.), wheel covers (Los Angeles), spark plugs (Toledo), seat covers and carpets (Albemarle and Gastonia, N.C.), catalytic converters (Columbus, Ind.), mirrors (Anderson, Ind.), decorative stripe tapes (Minneapolis), paint (Cleveland), light bulbs (New Hampshire).

Yes, the economic tinder is dry. But it may be dampened, first by the fear of, then by the fact of, red ink. Reagan's misplaced confidence in his program (and the state of the art of economic analysis) has taught him the difference between certainty and certitude. Perhaps good news will teach a similar lesson to the cocksure pessimists who are blooming with tropical luxuriance in Washington this winter.

What will happen? I do not know--which distinguishes me not at all from anyone. Some sort of recovery is stirring, but its strength and duration are unknowable. Perhaps whoever is president in 1985 will ride a rising curve. But perhaps Reagan will have been like Moses on Mt. Pisgah. On that mountain, Moses was given a vision of the promised land his people would reach but that he would not.