YOU CAN HEAR THE jackhammers all day long in the heart of downtown, and when you look up to the sky, huge cranes are feeding helmeted workers with the materials for more and more office buildings. But look beyond this healthy horizon and there is another story of commercial activity in the capital city--and for the city economy, it is disturbing. Here and there, one by one, big and small, businesses are packing up and heading across the District line or the Potomac to set up shop in the suburbs. They do so not as evil defectors, but as businesses with understandable interests in their own financial health.

Look at reports that have appeared in various sections of The Post over the last few days:

Sears, Roebuck & Co., closing its Northeast Washington store after 53 years; Woodward & Lothrop, considering relocating its downtown operations division (non-retail operations); Perpetual American Federal Savings and Loan Association, moving its 350-employee operations center to Alexandria; Hecht's, looking for another site for its downtown store, perhaps in the city, perhaps not; and major grocery stores disappearing--down from 91 in 1968 to 33 last year).

It is true, of course, that Greater Washington is just that--a region in which residents cross and recross state boundaries for all sorts of reasons beyond the old and vanishing "bedroom community" days of suburban homes and city work. In the two states, there are more and more people whose daily commutes are within their home jurisdictions instead of into the city. And businesses are likely to go where the markets are, and let the chips fall where the may.

If too many chips--sales-tax revenues and payroll checks--fall in the suburbs instead of the city, it is up to the District government, not the consciences or sentimentalities of business executives, to turn things around. And city administration officials are not oblivious; they have been examining strategies for retaining businesses. But unless initiatives are undertaken soon, the disappearances of outlets are likely to continue.

A "Business Retention Survey" completed last year by Brimmer & Co., an economic and financial consulting firm headed by Andrew F. Brimmer, found that, of 246 firms questioned, about half were considering moving all or part of their facilities from the District. Population and economic growth in the suburbs were cited, as well as less burdensome costs --including taxes and workers' compensation. Space for buildings, parking and one-stop shopping areas were other factors.

Lawrence P. Shumake, director of the city's Office of Business and Economic Development, noted in an interview with staff writer Sandra R. Gregg that there are some abandoned lots and federal surplus land--such as Camp Simms in Southeast-- that could be leased or sold to developers at attractive prices. And as Mr. Brimmer has suggested, there could be changes enacted to create a more attractive tax package for existing as well as new businesses.

It is not a matter of detracting from the economic health of the suburbs--but of attracting and retaining the commercial revenues and services on which so many residents and taxpayers of this region must depend for a livable and financially stable city.