The real estate tax rates for Arlington County were listed incorrectly in yesterday's Metro section. The rate per $100 of assessed valuation is $0.97 for 1984-85 and was $1.29 for 1979.

WHATEVER ELSE the good voters of Prince George's choose to do on Nov. 6, those who believe they have a stake in the county's future financial standing should rally and vote for approval of Question A on the ballot. The proposal is not the least bit radical, nor would it permit any part of local government to go on a spending spree. On the contrary, champions of frugality can see the importance of this ballot proposal, which is for a modest but critical adjustment of TRIM, the 6-year-old, inflexible cap on county property-tax revenue. And adjustment is the operative word here, because approval of the proposal would not repeal TRIM. On the contrary, it would improve the way TRIM operates.

Here's the troubling situation, and what the modification would accomplish:

The proposed amendment to the county charter would set controls on the property tax rate instead of continuing an unrealistic, outdated and inflexible dollar-amount cap on the property tax collections, which has been frozen (no matter what) at $143.9 million. The property tax rate would be set at $2.40 for each $100 of assessed valuation; that's three cents lower than the current rate. The difference would be that the county's collections could rise as assessments increase and new construction occurs.

True, taxpayers up to now have held fast, resisting any change in TRIM and managing to survive. And if people want to see how long it takes before the county's financial standing in general and credit rating in particular both hit rock bottom, they can vote to do nothing. They don't have to listen to the police chief, to responsible business leaders around the county or to those who seek to attract new business, new jobs and other ventures that prefer to locate where the economy is not threatened and the financial standing is tops.

Up to now, Prince George's County has been relatively wealthy and able to grow. As residents know, it is a diverse and attractive place in which to live and work. The local government, like its counterparts elsewhere, can always find new ways to cut unnecessarily high costs and make management more efficient. And the ultimate control here always rests with voters, who can reject those officials who do not perform respon- sibly. But for voters to continue saddling themselves and their government with an antique policy that limits the county's potential and threatens certain services would be reckless. That is why thoughtful residents are seeking help in winning approval of the moderate proposal in ballot Question A.