Weakening real estate markets around the country pose new dangers to the safety of the nation's banking industry because the level of real estate lending increased so much in the 1980s, bank regulators and industry analysts told a congressional hearing yesterday.

Real estate loans now make up 23 percent of banks' total lending activity, up from 15 percent at the end of 1980, said John P. LaWare, a governor of the Federal Reserve System, testifying before the House Banking Committee.

Bad real estate loans are on the rise, he said, climbing 37 percent last year and by another 8 percent in the first quarter, and they now account for fully half of all bad loans in banks' portfolios.

The committee is probing the extent of real estate-related problems within the nation's banks to try to determine what steps, if any, should be taken to prevent a savings and loan-like crisis in the banking industry.

"The savings and loan crisis -- with its megabucks costs -- has obscured developments in the banking industry and the deteriorating condition of the insurance fund that guarantees bank deposits," said committee chairman Henry B. Gonzalez (D-Tex.).

Conditions could get worse rapidly, depending on what happens to the nation's economy, said commercial bank analyst Charles Cranmer of Shearson Lehman Brothers Inc. Cranmer said that one-fifth of the nation's office buildings are vacant, but construction, although down considerably from recent highs, is still 50 percent higher than it was in 1979.

Nevertheless, the witnesses cautioned that factors other than declining real estate markets are also critical to the health of the banking industry. Banks' management abilities, their capital base, the health of their regional markets and their underwriting standards, combined with consistent and strong regulatory scrutiny, are equally important, they said.

The real problem for banks is that their powers need to be broadened so they can offer wider services, said Robert L. Clarke, comptroller of the currency. The central issue, according to some of the committee members, however, may be substantial revision of the deposit insurance system.

Potential pitfalls for the banking industry were highlighted by the much-publicized financial problems of New York developer Donald Trump, who has received $2 billion from more than 70 lenders. Some of the loans are reportedly unsecured.

Manufacturers Hanover Trust Co. of New York, in particular, is holding about $157 million of nonperforming loans -- ones on which interest is not being paid -- made to the Trump Organization, according to the Securities and Exchange Commission.

Gonzalez had asked Trump and officials from his four principal lenders -- Chase Manhattan Bank, Manufacturers Hanover, Bankers Trust and Citicorp -- to testify before the committee, but all refused, stating that they believed their financial dealings were private.

But several congressmen questioned whether Trump and his bankers are expecting American taxpayers to pick up the tab if the real estate ventures, including hotels and office towers in New York City and gambling casinos in Atlantic City, fail.

Trump "is gambling with taxpayers' money," said Rep. Bruce F. Vento (D-Minn.).

Banking regulators also declined to discuss Trump's lending policies, saying it is their policy not to discuss individuals and their financial situations in a public forum.