The federal budget deficit for 2013 reached $750 billion by the end of August, the non-partisan Congressional Budget Office estimated Monday.

The total is a $400 billion drop from the comparable period last year, a significant cut in the government's spending to revenue imbalance. At this point in 2012, the deficit stood at $1.164 trillion.

CBO said that with one month left to go in the fiscal year, the full year deficit by the end of September is expected to come is at a slightly lower number. The month of September is expected to feature higher revenues compared to spending, generating a surplus.

Deficit reaches $750 billion for 2013: CBO-thirds of the reduction in the deficit this year is due to higher revenues, CBO said. Revenues were up $284 billion. The New Year's fiscal year deal allowed income and payroll tax rates to rise and the economic recovery is also generating higher receipts.

Spending is down 4 percent, or $41 billion, the CBO estimated.

The CBO estimate comes as Congress is slated to kick off weeks of wrangling on the federal budget. The House is expected to pass a stopgap spending bill this week that would keep spending at current levels for two to three months despite Democratic efforts to reverse automatic indiscriminate cuts that started in March when Congress was unable to agree on a blueprint to change them.

By mid-October, Congress and the White House will need to come together on an agreement to raise the nation's $16.4 trillion debt ceiling. House Republicans want spending cuts or entitlement reforms in exchange for raising the ceiling.