Canberra — Newspaper promotion posters at sidewalk newsstands said, simply, ''rain.'' That message was the best that Australia could have wished to begin 1983. Rain fell this week on much of eastern Australia, where a crippling drought, combined with domestic and international recession, is producing the nation's worst economic outlook in 30 years.
The rain this week will not by itself alter that outlook, but the two to three inches that fell on much of the parched countryside was gratefully received. Another five or six inches over the next few weeks would be required to break the drought.
Acting Prime Minister Doug Anthony told Australians this week that the drought's full economic consequences are not yet apparent.
Federal and state governments are doing a great deal to help people, and this is costing taxpayers '' a lot of money,'' he said. But he added that more may have to be done.
''It would be a serious mistake to believe that farmers' problems are over, even if more good rain falls soon,'' he said.
Droughts are a recurrent theme in Australia. Agricultural economists estimate that over the past hundred years, one year in two has been a drought year, and really bad droughts, such as the present one, are likely every 15 to 20 years.
Federally financed dams and major water conservation projects have helped to ease some of the current difficulties, but most of the dams are at record low levels.
In some areas, the drought is entering its 47th month, making it among the worst in the nation's history. Its effects have been felt through 95 percent of New South Wales, and much of Queensland, Victoria, and South Australia.
Earlier government forecasts of a 20 percent decline in agricultural production in 1983 suggested that the country's economic output will slide backward for the first time since 1952-53.
Wheat production has fallen and throughout Australia will be 45 percent lower than last season. Sheep and cattle have also been affected by the drought. Some ranchers shot their sheep because raising and transporting them to market would have cost more than the income they would produce.
Several months ago the federal government announced financial aid of about $ 300 million to help the rural sector. It includes subsidies for fodder for sheep and cattle, and loans to tide over farmers and small businesses until agricultural conditions improve.
Cities, too, have been affected by the drought. Some have imposed water restriction, mainly limiting (sometimes to an hour a week) the watering of home gardens and lawns.
But city discomfort is nothing compared to country areas, where some rivers have dried up and water for domestic purposes has carted up to 50 miles.
Large grazing areas in the west of New South Wales are accustomed to having little water. They can produce sheep and cattle on nine inches of rain a year. But only three inches fell last year and much of this area missed the New Year rains.