The Civil Aeronautics Board tentatively decided yesterday to continue to require, by federal regulations, that airlines provide their passengers with a guaranteed no-smoking seat.

However, in a modification of its current rules, the board said the airlines wouldn't be required to provide seats in no-smoking sections for passengers who show up at the last minute. The airlines will be required to accommodate requests from travelers for seats in the no-smoking sections only if they have meet the check-in requirements the airline applies to all passengers.

The airlines have complained that the current rules, which require them to accommodate the requests of late-arriving passengers, can cause delays and inconvenience when other passengers must be shifted for the latecomer.

The board's members were divided on the matter, with two members arguing for dropping all the agency's smoking regulations. Both Chairman Marvin S. Cohen and George Dalley said they believed industry would accommodate the interests of nonsmokers with or without the CAB's rules. "I don't think the government needs to be doing this," Cohen said. Dalley agreed, arguing that an industry that can decide where to fly and how much to charge "should be trusted to accommodate the interests of their customers."

The majority felt that the public should continue to be protected by federal regulations to make sure the airlines do provide for the nonsmokers. "If you want to call it regulation, this is good regulation," Gloria Schaffer said. "The existing rule has worked amazingly well."

The board's smoking regulations have been in effect since 1973 and were modified in 1979.

The board's discussions came as Muse Air, a new Dallas-based low-fare airline, announced that it will start up next month as the first "no-smoking" airline.

In other aviation news yesterday:

Piedmont Airlines announced a new one-way fare of $71 on its one-stop service between Washington and Charleston, S.C. The move follows Air Florida's announcement that it will begin non-stop service between the two cities on July with a one-way fare of $99 on Saturdays and $118 Sunday through Fridays.

Texas International Airlines announced that it will begin non-stop service between Cleveland and both Houston and New Orleans on July 15. The move to Cleveland means that TI will fly for the first time to the same city being served by New York Air, its affiliate.