With 663,000 more jobs disappearing from the American economy last month, swelling the total number of jobs surrendered to the recession beyond five million, the government’s response to the downturn is being put to a strenuous test.

When drafting plans in January to spend roughly $800 billion to stimulate the deteriorating economy, the Obama administration operated on the assumption that the unemployment rate would reach 8.9 percent by the end of the year — without the extra federal spending. Three months into the year, the unemployment rate has already soared to 8.5 percent, from 7.6 percent, the highest level in more than a quarter-century.

Between January and March, more than two million jobs were lost, according to the Labor Department’s employment report, released Friday.

The severity and breadth of the job losses in March — which afflicted nearly every industry outside of health care — prompted economists to conclude that an agonizing plunge in employment prospects was still unfolding.