NEW YORK (AP) _ Concern about Chase Manhattan Corp.'s exposure to the nation's shaky real estate market triggered a downgrading of the credit rating of the nation's second-largest bank Monday.

Moody's Investors Service Inc. said it was lowering its ratings on about $7.6 billion of long-term debt of Chase Manhattan and its banking subsidiaries by one notch.

The downgrade was made as part of a review of all major U.S. banks prompted by concern about their exposure to the real estate market, said Christopher T. Mahoney, an associate director at Moody's.

''The U.S. is facing a cyclical real estate problem similar to what it had in the mid '70s,'' he said, ''and this time we may not be inflated out of it the way we were in the late '70s.''

The move comes on the heels of a similar downgrading of Citicorp, the nation's largest bank, by Moody's and another rating agency, Standard & Poor's Corp.

It also comes at a time when federal regulators have cautioned banks to be prudent in lending, particularly for real estate projects. Some politicians and builders have criticized the regulatory scrutiny, saying it has produced a credit crunch that could tip the economy into recession.

The national real estate market has deteriorated recently, particularly in the Northeast, Mid-Atlantic and Southeast, Mahoney said. ''Chase has a heavy weighting in those areas,'' he said.

Moody's estimates that Chase's $107 billion of assets, second only to Citicorp, includes roughly $9 billion in real estate loans.

The credit agency's concerns were mitigated somewhat by Chase's efforts to bolster its capital and cut unprofitable businesses, Mahoney said. The bank's credit standing continues to be supported by the diversity of its businesses and its holdings of undervalued assets, Moody's said. ''We're disappointed by Moody's announcement, particularly since Moody's acknowledged our capital- building activities,'' Chase spokesman Steve Rautenberg said.

The bank boosted its common equity capital - its cushion for losses - by $1.3 billion to $4.4 billion from October to March, Rautenberg said.

Rautenberg said he couldn't comment directly about Moody's concerns regarding real estate lending, but he did say Chase has emphasized fee- generating real estate activity such as private placements and syndications over direct lending recently. As a result, the bank's exposure to real estate hasn't increased significantly in the last year or two, he said.

The rating change shouldn't have ''any incremental effect'' on Chase's costs because the bank has little need to borrow long-term funds, Rautenberg said.

Thomas H. Hanley, a banking analyst with Salomon Brothers Inc., agreed. Although the bank's long-term debt was downgraded, its commercial paper rating was left unchanged, he noted. Banks are major issuers of commercial paper to obtain short-term funds.

The nation's banks are likely to be plagued by a weak real estate market for some time to come, Hanley said. ''I don't see any quick turnaround,'' he said.

Moody's lowered its rating on senior debt of Chase Manhattan Corp., the holding company, to Baa2 from Baa1. The rating on long-term deposits of Chase Manhattan Bank N.A., the main banking subsidiary, was lowered to A3 from A2. Ratings on other long-term debt of the holding company and its subsidiaries was dropped one notch.

Tanya Azarchs, a vice president at S&P, said her agency hasn't changed its ratings on Chase but was reviewing major banks largely because of the sluggish real estate market. ''It's a situation that does disturb us,'' she said.