WASHINGTON, June 4 (Reuters) - The U.S. budget deficit climbed toward $1 trillion during the first eight months of the 2009 fiscal year, hitting an estimated $984 billion as the recession firmly gripped the country, the U.S. Congressional Budget Office said on Thursday.

The non-partisan budget analysis for Congress showed that receipts from October through May were down an estimated 18 percent from the same period in 2008. The deficit for the same period in fiscal 2008 was about one-third, $319 billion.

Corporate receipts dropped by $108 billion, or 61 percent, during the first eight months of fiscal 2009 because of lower corporate profits and more favorable tax treatment for companies, the CBO said.

CBO has estimated that the budget deficit would likely crest at $1.8 trillion this fiscal year, blowing away previous records. CBO has forecast that the deficit would likely drop to almost $1.4 trillion in fiscal 2010, which begins Oct. 1.

The deficits have also expanded because of the $787 billion economic stimulus package Congress approved, as well as outlays for the $700 billion financial bailout program that has aided struggling banks and U.S. automakers. (Reporting by Jeremy Pelofsky, editing by Dan Grebler)