THE METRO BOARD, being composed of politicians, is troubled by the thought of political advertising in Metro. Should it be permitted? The board plans to take the question up today, and it seems to be leaning toward a flat ban. That's the wrong decision.

Metro has adopted the perfectly reasonable policy of permitting a limited amount of advertising in the subway and buses. But now it seems to be teetering on the brink of declaring that advertising commercial products is all right but advertising ideas or causes or candidates is somehow tainted and unfit for public places. That's a curious inversion.

Any kind of advertising in public space requires firmly enforced standards of taste and fairness. The Metro board is quite correct in assuming that those standards are harder to define in political ads. People's sensitivities are greater, they get angry more quickly. Metro is trying to avoid quarrels. Since Washington is a city that naturally attracts people with messages to deliver and causes to pursue, Metro fears - no doubt correctly - that it will be confronted with issues of propriety that might not arise in other cities. But those issues are not insoluble. Access to public attention is an important public value anywhere, and nowhere more than here.

What about the candidate with the heavily financed campaign who tries to preempt all the available subway space? It's perfectly possible to limit the space sold to any one candidate. What about an inflammatory ad on one side or the other of a deeply felt question - for example, the morality of abortion? Deliberately inflammatory ads can be refused on grounds of propriety. Beyond that, it's necessary to say that riders do not have an unlimited right to be protected from disturbing or irritating views.

Political advertising, it has to be recognized, can mean more than the usual vote-for-Doe placards. There might be ads aimed at foreign governments - opposing, to take a familiar example, the shah's rule in Iran. Within the bounds of decency, its better to let those voices be heard. It's sometimes hard on people's sensibilities, but the tradition in this country has been to let people deliver their messages. It's a good tradition, and we'd be sorry to see it shut out of Metro.