With interest rates coming down, home buyers are beating a path to the bankers' doors. Lower rates mean that it's easier to qualify for a big mortgage loan, hence easier to buy the larger house you had in mind.

But some of you will be disappointed. Lenders are suffering one of their periodic attacks of old-fashioned prudence -- and have tightened their rules on who qualifies for a loan.

If your income looks marginal relative to the size of the loan you want, your banker is now more likely to say no than yes. You can still get a mortgage, but perhaps one not as big as you had hoped.

The lenders have reason to be cautious. Real estate prices are not rising as quickly as they did in the past; in many cities, prices are actually going down. If you run into a bad financial patch, you might find that your house is worth less than the mortgage you're struggling to pay -- which is encouraging more strapped families to mail their house keys to their bankers and walk away.

The default rate on mortgage loans has reached a record high of 6.19 percent (7 to 8 percent on FHA and VA loans).

Christopher Kallen, a vice president of First Wisconsin National Bank in Milwaukee, says that the modern two-income family adds to the risk for mortgage lenders. Both incomes are counted when deciding how large a loan the couple can handle. So now there are two chances, instead of one, of losing a job in the family, and subsequently losing the house.

But despite all the flashing yellow lights, bankers still want to provide you with a mortgage loan. That's the way they make money, and they'll listen to any reasonable proposition. Here are the rules of thumb for showing that you're a good risk:

*Don't ask for a much larger loan than your income can support. Generally speaking, your monthly housing expense (principal and interest payments, taxes, insurance and dues, if you live in a condominium) shouldn't exceed 25 to 28 percent of your stable monthly income.

Your total monthly obligations (for housing, payments on installment debt that extends beyond 10 months, mortgages on other non-income-producing property, alimony and child support) shouldn't top 33 to 36 percent of your monthly income.

Lenders may fudge these standards a little bit when you're buying a first home. But for a second home, expect them to be strictly enforced. Real estate agents have loan repayment books that will help you establish how large a loan a lender might give you.

If you want a larger loan than the standard guidelines would allow, you have five alternatives:

First, try another lender. Each bank, S&L and mortgage banker has slightly different standards -- so one may grant the very same request that another turns down. Your real estate broker should be able to steer you to the most liberal lenders in the area.

Second, try to raise your income. Show your banker that you have a guaranteed raise coming up, or that your spouse is due a promotion. Some one-earner couples get their loans by finding the at-home spouse a job.

Third, try to reduce your other debt. Just by squeezing down expenses for a few months and paying off a car loan, you might reduce your total monthly payments to a level acceptable to the bank.

Fourth, produce strong evidence of your ability to handle a higher mortgage payment. Maybe your alimony payments will end in a year. Maybe you have substantial savings that you prefer not to put toward the down payment, but that are available in an emergency. Maybe you have a solid history as a saver who rarely goes into debt.

Fifth, judge the neighborhood carefully. Lenders rarely give maximum financing in an area that is less than 25 percent improved or that is changing from residential to commercial.

Save up more money for a down payment. Today's tougher standards apply chiefly to borrowers who can afford to pay only 5 to 10 percent of the home price in cash.

*Lenders are doubly cautious if you want to combine a low down payment with an adjustable-payment mortgage. They're afraid you might lose your incentive to pay if the value of your house goes down at the same time that your mortgage payments go up.

For your first house and even your second, bankers say that there's nothing better than today's version of the G.I. Plan. That means Good In-laws, who are willing to kick in some cash to help you get a mortgage you can afford.