Robert Dederick will be nominated as undersecretary for economic affairs at the Commerce Department as part of a move to upgrade the economics staff at Commerce, the White House has announced.

Dederick, 52, was assistant secretary for economic affairs until last week, when President Reagan signed into law a bill abolishing that post and creating the undersecretary's post. Commerce Secretary Malcolm Baldrige has been moving for several months to raise the status of his economics staff. Baldrige has become more involved in economic issues than other Commerce secretaries, sources say.

Dederick, who was assistant secretary for a year, will be the third undersecretary at Commerce, joining those for international affairs and tourism. Chief Economist Robert Ortner, who works for Dederick, will now have the rank of assistant secretary, a Commerce spokesman said. This is "quite a change" from the days when the top economics position was below the rank of assistant secretary, the official added.

Dederick and Ortner both discuss economic issues more in terms of traditional Keynesian analysis than of either supply-side or monetarist theories. The Commerce Department took a more pessimistic view of the economy than the Treasury, where supply siders originally dominated economic forecasting, sources have said.