In the first comprehensive investigation of its type, federal researchers have found that a "significant percentage" of American home mortgages -- more than 10 percent -- carry excessive escrow accounts under federal guidelines.

But the study by the Department of Housing and Urban Development concludes that the vast bulk of loans carry lower escrows than legally permitted, and that mortgage companies frequently have to advance their own funds to pay portions of homeowners' property tax and insurance bills.

If mortgage firms were required to return all excess escrows to borrowers immediately, the new study said, homeowners nationwide would receive from $700 million to $1.6 billion. But if lenders raised their escrow charges to the maximum levels allowed under federal law, American homeowners would have to pony up another $8.2 billion to $11 billion in their mortgage payments.

Conducted during 1991 and 1992, the HUD study provides the first hard, statistical evidence documenting the escrow practices used on millions of home loans. Mortgage escrow accounts are one of the hottest consumer issues in the housing field. Out of 40 million residential first mortgages and deeds of trust nationwide, about 78 percent have escrows, according to Census data.

Homeowners' monthly payments on mortgages with escrows are divided into two parts: Most of the payment covers interest charges and principal reduction. But a portion is set aside in a separate pot -- the escrow account -- to handle upcoming property tax, insurance and other periodic expenses. Out of a monthly mortgage payment of $1,500, for example, $1,200 might go for principal and interest. The remaining $300 goes into the escrow. When tax bills come due during the year, the escrow should have sufficient funds accumulated to pay the correct amount.

Under federal law, mortgage companies are permitted to make monthly escrow charges equal to one-twelfth of the total anticipated annual property tax, insurance and other costs covered by the account. They also are allowed to build up a two-month "reserve" or cushion to handle unexpected increases in those costs. At least once during the course of the year, the balance of funds in the escrow account must drop to the two-month reserve level or lower.

Criticism over lenders' escrow practices has been intense since 1990, when the attorneys general of 12 states accused the home mortgage industry of illegally padding their escrows, and overcharging consumers billions of dollars per year. The attorneys general sued the third largest mortgage servicer in the country -- General Motors' GMAC Mortgage Corp. -- in December of that year. In January 1992, GMAC agreed to a settlement of the class-action suit, but insisted that its escrow practices conformed to federal standards. Refunds or payment reductions under the GMAC settlement have been estimated to total as much as $100 million.

The attorneys general have since been in settlement negotiations with other large, national mortgage companies, including Fleet Mortgage Corp., but have filed no additional suits.

Congress also has jumped into the escrow account issue. The chairman of the House Banking Committee, Rep. Henry Gonzalez (D-Tex.), has reintroduced legislation that would require lenders to pay interest on all escrowed funds, and to allow borrowers to opt out of escrows when their mortgage balances drop below 80 percent of the original principal amount.

The research in the new HUD study covered 220 mortgage servicing companies nationwide who collectively administer the loans of 28 percent of the 31 million homeowners with escrows. Investigators directly examined more than 8,400 randomly selected loan files in depth.

Among the key findings:

Only 4 percent of the mortgage firms used escrow computations that routinely result in excessive charges to borrowers. Some of those overcharges were huge -- six to nine months' worth of payments higher than legally permitted -- but the bulk of overpayments were in the one-month or less range.

The escrow computation method used by the vast majority of mortgage firms -- the "single-item" approach -- is legal under federal statutes and is not, in and of itself, the cause of most overcharges. This directly contradicts the charges of the state attorneys general, and could derail settlements under negotiation with major lenders.

Mortgage industry under-escrowing actually costs lenders far more per year than over-escrowing costs consumers. Nearly one-quarter of all escrow accounts require advances of money from lenders' own corporate funds during a typical year -- money that lenders have to collect from borrowers by either raising subsequent monthly escrow withholdings or by requesting lump-sum payments.

What's the upshot of the new federal study for you as a borrower? While there's a "significant" chance you're handing over too much per month for your escrow, there's apparently a far better chance -- believe it and wince -- that you're actually paying less than you could.