President Obama sent Congress on Monday a proposed budget of $3.8 trillion for the fiscal year 2011, saying that his plan would produce a decade-long reduction in the deficit from $1.6 trillion this year, a shortfall swollen by $100 billion in additional tax cuts and public works spending that he is seeking right away. But at the end of the decade, the yearly deficits would begin moving up again, as the projected costs of health and retirement programs for an aging population start to escalate, according to forecasts in the administration’s new blueprint.