If all goes as scheduled, the Metro board will adopt an implicit policy today that bus passengers should conform their riding habits to traveling between two points along the routes laid out by the transit system--in some instances, as long as 121 years ago. If a route doesn't go where the rider is destined and he must transfer from one line to another, it would cost 5 cents extra.

The impact, if the board adopts its staff's proposal for a transfer fee on top of a basic nickel fare increase, will be felt most heavily on those otherwise least mobile in the District of Columbia. It means that a mother living, say, in the Trinidad section of the city must pay extra to transfer from one bus to another to take her child to a clinic at D.C. General Hospital.

For Washington bus riders, the fare-plus-transfer increase will amount to 23 percent higher fares, according to Gladys W. Mack, a mayoral aide and Metro board member. The increase has been endorsed by Mayor Marion Barry as a way of reducing the bus system's huge deficit. There would be no charge, however, for transferring from the subway to a bus. Basic subway fares also would rise.

A few of the oldest Washingtonians may remember that the old D.C. Public Utilities Commission agreed in the spring of 1919 to let the two streetcar companies charge 2 cents for transfers atop the basic 5-cent fare. Just six months later, apparently the result of community outrage, the commission agreed to raise the basic go-anywhere fare to 7 cents and to restore free transfers.