NEW YORK, April 1 (Reuters) - Corporate America’s credit quality collapsed in the first quarter, with Moody’s Investors Service downgrading an estimated $1.76 trillion of debt, a record high, the rating agency said on Wednesday.

The downgrades included a record number to the lowest rating categories, signaling the approach of the worst defaults since at least World War Two, Moody’s chief economist John Lonski said in an interview.

“These are numbers that just underscore how risky both the financial and economic environment remain,” Lonski said.

The downgrades reflect how badly corporate balance sheets have been hurt by the slump in consumer spending amid the deepest economic contraction since 1982.

“Business sales and profits fell off the table in general during the final quarter of last year and have continued to deteriorate in the first quarter in 2009,” Lonski said.

U.S. corporate profits plunged a record $120.1 billion in the fourth quarter, depressed by tumbling consumer spending and exports.

Downgrades of investment-grade companies shot up by 153 percent from the year-ago quarter to a record 96, while downgrades of junk-rated companies surged by 147 percent to 287.

The rating downgrades were led by industries with exposure to the ailing housing industry, including homebuilders, mortgage insurers and major money center banks. Some 70 of the quarter’s downgrades were housing related.

“The most prominent new driving force behind credit rating reductions would be deterioration of commercial real estate,” Lonski said. That is taking a toll on regional banks and companies that manufacture equipment and material used in construction, he said.

The downgrades included one of the largest on record, $326 billion of bonds and preferred shares of General Electric Co GE.N and its units. Other major borrowers downgraded included Ford Motor Co F.N, Citigroup C.N and Bank of America BAC.N.

In addition to housing, sectors under rating pressure included automakers and auto parts suppliers, media companies, casinos and retailers.

Among the downgrades were 22 fallen angels, or companies cut to junk status. In addition, 82 ratings were downgraded to the lowest categories, Caa3 or lower. That means that the U.S. high-yield default rate, which stood at 5.7 percent in February, is destined to climb sharply in short order, Lonski said.

Moody’s has forecast that the U.S. default rate will peak around 14.5 percent in November. (Reporting by Dena Aubin; Editing by Leslie Adler) (dena.aubin@thomsonreuters.com; +1-646-223-6325; Reuters Messaging: dena.aubin.reuters.com@reuters.net))