The nation's big-city mayors have every reason to envy Marion Barry.

Washington's present political and economic climate, I believe, gives our new mayor opportunities other cities lack. He could make this city a model of interracial cooperation. And taking advantage of the surprising building boom, he could make visible improvements in the housing and living conditions of the city's poor.

What it takes, as the mayor well knows, is the rare combination of idealism and pragmatism that makes for statesmanship. Not everyone in Barry's entourage, however, shares the unprejudiced, undogmatic flexibility successful leadership requires.

The first premise, a big-city mayor anywhere must realize nowadays, is that the city's problems cannot be solved within the city limits. Urb and suburb must work together to share the wealth and opportunities of the metropolitan region. That means, first of all, that the suburban counties will have to overcome their prejudices against the center city on which they depend.

But it also means that the center city must think and act in the regional context and, more specifically, that Mayor Barry become not only a whole-hearted participant, but a leader in the Washington Metropolitan Council of Governments. Washington's COG is probably the most enlightened in the country. This region works well together on Metro and other regional concerns.

It would be detrimental to this cooperation, however, if Mayor Barry were to persist in candidate Barry's notion that all employes of the District should live in the District. Suppose Fairfax County were to pass a law like that? Since only five percent of its residents are black, only five percent of county employes would be black and His Honor himself would rightly raise holy hell.

The ideal that we ought to pursue in this country is that everyone -- black, white or brown; rich, poor or middle-class -- ought to be able to live where or how he or she pleases.

This leads me to another apprehension about the Barry administration: the automatic assumption that condominiums are only for the rich and evil and that low-yield or nonprofit cooperatives are for virtuous people of limited means and therefore good.

Not necessarily. Each case is different. The city's aim must be to provide as much housing for all income groups as possible and to make especially sure that people with limited incomes, and elderly persons with fixed incomes, have good homes and are helped to own those homes.

The city should therefore encourage apartment ownership, and that means condominiums. They appreciate in value and give the owner a little slice of the blessings of capitalism. They offer some protection against inflation. Low-yield apartment cooperatives, although they may also be virtuous, rarely manage improvements or appreciate in value.

The city, I believe, should take a positive attitude toward apartment house living for those who like it. Apartment houses are more energy-efficient than single family homes. Besides, we have so many of them. It seems to me silly to inhibit their improvement with a "speculator tax." That will just drive developers to the suburbs. It seems to me a mistake to assume that all developers are ipso facto "the enemy."

Where privately owned apartment houses are to be improved and turned into condominiums, the city ought to help poor tenants, and particularly the elderly poor, to stay in them by giving low- or no-interest loans to be repaid when they sell or die.

A further important step in improving housing conditions in this city, as Barry's Housing and Community Task Force told him, is to improve the buildings and management of public housing.

Washington has its share of rotten landlords who exploit the poor. But the most scandalously rotten of them all is Washington's National Capital Housing Authority.

There is a danger that uninformed or dogmatic rhetoric will get in the way of constructive redevelopment. The current rhetoric is about "gentrification." The very word suggests an anti-middle-class bias, fashionable with bearded, leftish middle-class sociologists but silly when we deal with the real and predominantly middle-class class world.

Specifically, "gentrification" denotes the recent phenomenon of white middle-income people buying deteriorating old houses in the low-income areas in town and rehabilitating both the houses and the area. It is the best thing that has happened to American cities since ditches were turned into sewers.

No doubt rehabilitation often displaces poor families, who either own the old houses and lack the means to fix them up themselves or who rent them and are forced out by their landlord.

Good city government must deal with displacement. But it must deal with this complex issue in a cool, practical, helpful manner and not allow it to become an emotional issue that blocks the rehabilitation movement.

In the first place, displacement due to rehabilitation may not be as widespread as Mayor Barry was told. His task force said approximately 150,000 families were in danger of being thrown out of their houses. The Census Bureau just told us that the city lost population. Could it be that many of these endangered families have displaced themselves -- to Prince George's County?

In the second place -- and I realize this is an easily misunderstood statement -- properly assisted relocation is often desirable. The low-income ghetto offers few, if any, opportunities for its residents to improve their lot. The city's, the region's and the nation's foremost urban aim should be to bring people and jobs together.

Rather than getting upset about middle-income people breaking up the ghetto, we should help accelerate the effort and help low-income people out of the ghetto. This means using every available means of providing subsidized housing elsewhere in the region

To be sure, many families will want to stay where they are. But they will also welcome more affluent neighbors and a chance to improve their homes and their lives. That chance must be offered through low-interest rehabilitation loans.

The opportunities for turning Washington into a livable city for all are greater than they have been in the city's entire history.

Let us hope Mayor Marion Barry seizes them.