Kirstin Downey's fascinating and meticulously researched three-part series "The Manipulators"{front page, Sept. 2-4} on how housing speculation, fraud and the failure of government oversight destroyed the Trinidad area in Northeast Washington (as well as other neighborhoods) inferentially makes a telling point that the articles themselves never explicitly state. And that is the crucial importance of rent control -- even the weak version the District has -- in aiding poor and working-class people, saving their neighborhoods and retaining the city's dwindling stock of affordable housing. After all, the various schemes and scams the writer catalogues all had as their central feature the evading of the city's rent-control statutes.

Another important theme -- and lesson -- mentioned once in the series but needing underlining, is the role of "the bureaucratic, political and budgetary climate {at HUD} through most of the 1980s." The Reagan administration cut HUD staffing (both directly and indirectly, as so many good people left in disgust at the undermining of the agency's historic mission), and, like so many similar actions in the name of "getting government off our backs," it resulted in private sector irresponsibility and criminality. We are all now paying the bill for this mess.

Incidentally, Sarah Lyon and Hilton Green, the HUD employees whose dedication and persistence uncovered the whole smelly mess, deserve some kind of medal. CHESTER W. HARTMAN Washington

I commend The Post for its excellent series on the real estate vultures in Trinidad.

However, I think it should be pointed out that this mess was made possible by the jackals who decreed rent control. I do not quarrel with the government's helping out poor folks with their rent when factors beyond their control make it unaffordable. This should be done. But this should be at the expense of the taxpayers, not at the exclusive expense of the owners.

The laws of supply and demand cannot be repealed. They may be suspended in an emergency, but only for a short time. It was indicated that one apartment went from $95 to $700 a month when controls were removed. Obviously, rent control was robbing the owner of the worth of his property.

Rent control immediately stops the building of new units, because they will be unprofitable. Demand increases for old units, which despite controls, increase in value and eventually in cost to renters.

Renters are ill-served by something that unduly causes rental costs to rise. RAYMOND S. HALL Falls Church