THIS WEEK, the D.C. City Council took an unexpected plunge back into the thickets of rent control and emerged - by a slim 7-6 margin - with a vote to amend existing rent-control legislation by allowing across-the-board rent increases of 2 to 10 per cent. Several days earlier, the council had extended the current legislation - due to expire Oct. 31 - until January 1978. That action not only gives continued life to an already unworkable system, but also delays the day of new and tough-minded approaches to the city's housing problems. The best that can be said about this amendment is that it somewhat tempers the worst effects of the legislation that was already in place.

The rental-increase amendment was not schedule for council action on the day it was passed; it had been discussed and rejected at an earlier meeting, along with a more comprehensive rent-control bill. But while it may have been a surprise, procedurally, the idea of rent increases is hardly new. Months ago, the Rental Accommodations Commission, that group of landlords and tenants who are supposed to monitor the progress of rent control, had suggested this very measure. Unfortunately, in the emotional atmosphere that builds up whenever rent controls are discussed, the council gave the question something less than an objective and dispassionate examination.

It is no casual thing to allow rent increases in what is already one of the highest rental markets in the country, and we are certain that the council members who voted for the increases do not take the city's housing situation lightly. Rather, they seem to understand well enough that rent control is not necessarily designed to keep rents static. In the best of times, it is supposed to be a method of balancing not only the rental payments but all the costs borne by both landlords and by tenants. In a market where most costs other than the rent - and especially utility costs - are steadily rising and not controlled by the government, finding such a balance while holding the lid on rent increases is almost impossible. Without it, the whole concept of rent control collapses - and the reactions of a lot of people who are injured in the process are understandbly oversimplified and emotional. Thus we have Councilman Douglas Moore threatening to sue the city over this latest rent increase amendment, and a general tendency on the part of a lot of affected citizens to see the issue of rent control in terms of good guys (tenants) against bad guys (landlords). Now there are some slumlords in the city, as in most big cities. But they are not the majority of realtors - many of whom have been working with the city to try to work out some workable rent-control system. That has yet to be achieved - if, indeed it can be, short of a far more sweeping overhaul of the rent-controlsystem than has yet been attempted.In the meantime,the mayor should sign the legislation - amendment and all. The council is then going to have to plunge back into the rent-control thicket in an effort to clean it out in a much more deliberate and comprehensive way