It is the toughest challenge facing millions of would-be home buyers: How do you overcome those circumstances, often unique to each individual's situation, that stand in the way of purchasing a house?

How does someone who has a first job but no credit history get past the punitively low scores imposed by most lenders' electronic credit-scoring systems?

How does a single working mother, with little or no cash for a down payment and high monthly bills, convince a bank that she is a solid bet for a mortgage?

How does the newly minted doctor, fresh out of medical school and neck-deep in student loan debt and other bills, find a home loan at a market rate?

How does an immigrant family, dependent on pooled but only partially documentable cash income, demonstrate creditworthiness?

The answers to questions like these are the American home building and mortgage industries' equivalents of the search for El Dorado. And there is gold involved in this quest. Vast numbers of people would buy houses if they could be evaluated as creditworthy individuals who simply don't fit the traditional molds.

Every major institution in the home finance industry, from Fannie Mae and Freddie Mac to mortgage insurers and lenders, is working on techniques to "see through" applicants' special circumstances. The dominant credit-scoring technology firm, Fair Isaac Corp., is developing new tools to evaluate nontraditional credit histories by checking rent-payment records, telephone bills and utility payments. PRBC Corp. of Annapolis (Pay Rent, Build Credit) is attempting to become a national credit bureau for people who have minimal or no traditional credit histories with banks, card companies and the like.

Now one of the highest-volume national mortgage lenders, Countrywide Home Loans, has developed what might be called the all-season special-circumstances mortgage: a single program that translates the key elements of nontraditional financial profiles into traditional terms for mortgage underwriting purposes.

Countrywide plans this month to launch the new loan concept, called the Optimum mortgage, through its retail offices and network of participating brokers. It is not a program for people who truly cannot afford a house or don't pay their bills. It is an attempt to offer flexible standards in place of traditionally rigid loan requirements and to offer nontraditional applicants the same interest rates and terms that prime market borrowers receive.

The key special circumstances include:

* A sharply decreased focus on traditional credit scores. Using its in-house LandSafe Credit subsidiary, Countrywide plans to pull together and substantiate applicants' rent, utility, cable television, telephone and other regular payment records. Dottie Sheppick, senior vice president of strategic products, said LandSafe can check out most nontraditional credit histories and produce a credit-score proxy for electronic mortgage underwriting within 48 to 72 hours at a cost of $30 to $55.

* Recognition of the contribution of pooled family savings or community funds as down-payment sources. Traditional loan-underwriting standards require applicants to demonstrate that their down-payment cash comes from their own personal assets. Yet many households, particularly those of immigrants, depend upon pooled family resources or community funds to assemble down-payment cash.

* Use of "boarder" income to qualify for monthly payments. Many would-be home buyers make good money but not enough to qualify for a mortgage. Yet they may already provide living space to a boarder who contributes to the monthly household income. Traditional underwriting rules don't take such supplementary income into account for qualifying purposes. The new program will, provided the boarder has been contributing income to the household for at least 12 months.

* Recognition of hard-to-verify regular cash income from sideline work such as child care, cleaning services, landscaping, and auto or home repair. Again, traditional underwriting rules usually turn a blind eye to these frequently substantial additions to borrower income.

* Permission for nonoccupant "co-borrowers" to add some of their incomes to the primary home buyers' monthly income to qualify for the mortgage. Sheppick says these co-borrowers usually will be "people with longstanding relationships" with the applicants, such as an uncle or grandparent.

The new special-circumstances loan program will allow minimal down payments -- as low as zero if the borrowers have $500 in cash assets on hand -- and will offer the full range of standard fixed-rate and adjustable-rate loan terms. The maximum loan amount is $333,700 for a single-family home. Borrowers will need to have valid Social Security numbers and be either U.S. citizens or permanent or nonpermanent resident aliens. Some versions of the program may require home buyer counseling.

The essential thread running through this and other forthcoming efforts to expand the reach of mortgage financing? Help lenders translate your special circumstances into the language of modern mortgage-making, and you just may be able to buy a home.

Ken Harney's e-mail address is