THE BIG NEWS for most of the arts in this year's fall season is the economy: hangovers from its bygone downs and a surge reflecting its more recent ups. In practical terms this means an unusual emphasis on sure-fire attractions or low-budget performances: movie stars in plays at the Kennedy Center, road companies of market-tested musicals at the National and the Warner, classic plays in local theaters and a lot of action from local dancers and musicians who cost little to present.

A return of affluence seems to be reflected in pop music and movies, where attractions can be brought in on relatively short notice. Old rock acts are getting together again and hitting the road, and New Music America will bring to Washington a 10-day festival of music (with some dance and hard-to-define happenings) that will cross the borders between popular and classical art.

At least one movie scheduled for release this fall may affect the 1984 presidential election. A few others should be artistic successes. Ticket sales, already high, may be expected to surpass last year's.

In classical music, as in dance and live theater, plans involving big-name performers or large performing groups must be made long in advance. Relatively modest seasons are being forecast in these arts--reflecting the state of the economy when the plans were being made.

Museums and art galleries, which generally do not de- end on ticket sales, are planning their seasons approximately as in the past. "Whistler's Mother" and Leonardo's "Last Sup- per" will be among the arts newsmakers in Washington this season, but there will also be a show of sculptures that make noise. Also sure to make noise are a few blockbuster shows such as "Art of Aztec Mexico" at the National Gallery and "A New World: Masterpieces of American Painting" at the Corcoran.