Two authoritative government agencies reported this week that retiring baby boomers have contributed heavily to the shrinking of the nation’s workforce, countering fears that the recovery from the financial crisis has stalled out.

Before the recession hit, the labor force participation rate — the percentage of working-age Americans working or looking for work — stood at 66 percent. It has since fallen steadily, dropping to 62.8 percent as of December, the lowest reading since 1978.