PRESIDENT REAGAN has taken office as the United States enters a new era. The door to that era has been flung open by what Reagan last week called the worst economic mess since the Great Depression. At the aheart of the problem is the condition of our major cities, which house the majority of the ultrapoor. The urban poor are trapped in a system which offers them insufficient handouts on the one side, and on the other, dead-end jobs.

It is nothing new to say that inflation hits the poor the hardest. But lately, inflation has gotten so bad that the middle class has added its collective voice to cry for help. Reagan's economic package will rely on two basic measures, tax-cuts and expenditure cuts, to cure the nation's now chronic ills of low productivity and low growth. Legislators should concentrate their efforts on making sure that cuts in federal programs are aimed not at those who can least afford them, the urban poor, but at inefficiencies in the government bureaucracy, and especially the Defense Department. They should take a gradual approach to the proposed tax-cuts, and the supply-side economic theory on which they are based.

But legislators must realize that the economic policies of the last decade have not only failed to eradicate poverty, but also have boxed a majority of the poor into a no-win situation, while contributing to the current inflationary spiral.

Some would overlook the cause of today's crisis and have us believe that an even greater government role in the market-place could provide a solution; they suggest price-controls as one alternative to Reagan's plans. Far from curing the root causes of inflation, price controls temporarily ease its symptoms at the cost of each individual's loss of economic freedom. When price controls are removed, the economy will return to at least its former, possibly worse, inflationary condition.

Some, however, would advocate a permanent government role in setting wages and prices, as well as other features of a typically socialist economy. The essential choice that faces the country today is between this socialist view, and a vision for which Reagan is often criticized. It is a view of a healthy America made strong by productive individuals who live in a free society of limited government. If Reagan's plan fails, if the current crisis continues, the nation will most likely react by turning to socialism. But it will do so only after a wave of unparalleled social upheaval among the nation's urban poor. With constructive guidance from Capitol Hill, Reagan's plan may provide a way out--for both the impoverished and the soon to be poor--which preserves our traditional individual freedoms.

Simply because much of Reagan's package is new and untested, many steadfastly oppose it, offering instead programs which they have seen proven as failures. The unknown can often be frightening, but an America where the ideal of individual liberty has been sacrificed because we lost our courage to innovate is far more terrifying.