If you've seriously tried to comparison-shop for mortgage money this year, you've probably run into one of the most perplexing consumer challenges of the home real estate field:

With dozens of lenders active in even small-market areas -- each with a counter full of fixed- and adjustable-rate loan options -- how do you make sensible choices? How do you pinpoint lenders with superior rates and terms, without spending weeks on the phone, flipping Yellow Pages until your head spins?

Consumers in 140 cities could have at least a partial answer on the way. It's a sophisticated money-searching computer system tied into multiple-listing services (MLS) run by local realty boards.

Portions of the Washington, D.C., metropolitan market, Phoenix, Memphis and Tacoma, Wash., already have gone on line with the program. St. Louis will plug in next January, and 15 other metropolitan areas are expected to in coming months.

The new mortgage-money search system is the creation of McLean-based Planning Research Corp., the high-tech company that pioneered the computerized multiple-listing service in the 1970s. Its system dominates the electronic MLS field, accounting for the lion's share of urban markets in the United States.

The mortgage information program -- dubbed Loan Express -- "is the logical next step" after computerizing property listings, said Steven Polley, president of the Planning Research subsidiary behind the concept.

It takes consumers step by step through "an objective analysis of what's available in an entire mortgage marketplace" and brings buyers together with the lender they've identified, Polley said.

Once a local realty board decides to tie electronic money-shopping in with its MLS computer system, Planning Research Corp. signs up large and small lenders in the metropolitan area and equips them with computer terminals.

Lenders pay fees averaging $450 to $700 a month to be part of the system. Because it potentially brings their mortgage products onto every computer screen in every broker's office that uses MLS in an area, competitive lenders have jumped at the chance, according to Polley.

In markets where the electronic mortgage-shopping program is fully operational, lenders who account for well over half of the total annual loan volume in the area have signed up, he said. Every participating lender can list its full array of loan types, sizes, rates, indexes, payment plans and fees on the system, changing the data an unlimited number of times to keep it fresh.

Consumers pay nothing. They walk into a broker's office, explain what they're after, sit down with an agent and punch in their financial profile.

For example, let's say you're an upwardly mobile, second-time home buyer. You and your spouse have a combined, pre-tax income of $60,000 a year, and you've accumulated $20,000 in equity and cash for a down payment and settlement costs.

The computer financial analysis tells you in seconds what you and your spouse can buy: a $150,410 house in the area, using a one-year, adjustable-rate mortgage at 9.5 percent; a $130,640 house with a 30-year, 11.5 percent fixed-rate loan; or a $126,000 condo with a $113,000 mortgage at 12 percent. Those are just three of the dozens of financing packages available to you from local firms.

But what about the "right" loan for your pocketbook and tastes? How about bargain deals available from lenders you may or may not have heard of?

Here's where the electronic money search really can pay off. Let's say you're moving to a city already on line, such as Phoenix. You want to know not only if there are mortgages available in your price bracket that carry a better-than-average rate, but also if they include extra consumer protections.

For example, let's assume you want a single-digit interest rate, no more than 3 points (a point equals 1 percent of the sales price) in lender's fees at settlement, no higher than a 10 percent down payment, no negative amortization, maximum protection against rate increases and the right to convert the loan to fixed-rate.

The computer searches the Phoenix mortgage market's 700 distinct loan packages and comes up with an answer for you: There's only one lender, with only one mortgage option, that precisely fits your specifications.

The mortgage happens to be a 9.8 percent, $115,300 adjustable-rate loan, indexed to one-year Treasury bills. It comes with an unusually generous ceiling on interest-rate increases: 1 percentage point a year. In other words, you're guaranteed to have no worse than a 10.8 percent mortgage for your second year, and 11.8 percent for your third.

Three years down the road, moreover, you'll have the option to convert the mortgage to a fixed-rate plan.

The Loan Express computer prints out every key comparison-shopping detail of the loan, from its rate-cap terms to the address and phone number of the lender.

After that, it's up to you.