The Federal Home Loan Bank Board yesterday gave final approval for savings and loan associations to establish service units across state lines. This gives the thrifts an edge over commercial banks which cannot do so yet, except in special cases.

But don't expect S&Ls to have automated teller machines dispensing cash to appears overnight on Washington-area street corners. "In today's [troubled] climate, it is less likely," said Thomas Owen, chairman of Perpetual American Federal Savings and Loan. Perpetual is one of the special cases, having branches across the District line in Maryland which existed prior to a prohibition against interstate branching. So the S&L has had automated teller machines in both jurisdictions for some time.

The significance of this decision for Perpetual is that it now can set up machines, if it desires, in Virginia or any other state. Owen said yesterday the association is considering setting up terminals elsewhere but it has no definite plans.

That was the word also from Baltimore Federal. Citizens Savings and Loan has six terminals in Montgomery County. An official said yesterday it has no definite plans for more and has never considered expanding into Virginia or the District.

Guardian Federal, which has offices at Dupont Circle and Wheaton Plaza, will install automated teller machines in them next month. Matthew Warner said Guardian also is looking at the possibility of setting up a remote service unit at Lake Forest.

Remote service unit is an umbrella term that covers a number of electronic banking devices, including the automated teller machine in or outside a branch office, the cash-dispensing machine situated away from the office as in a Metro station, and the point-of-sale terminal located in stores to allow the customer to pay directly from his account.