If you seriously believe that American housing is a superior investment, you'll get a chance to put your money where your mouth is -- Wall Street style -- early next year.

The first national mutual fund designed solely to invest in home mortgages is being quietly readied here and in Boston and Philadelphia for a major launch next spring.

Its sponsors refuse to talk about it, citing possible problems with federal securities regulators. But finance-industry and Wall Street sources familiar with the project say that the fund represents the most ambitious effort in decades to guarantee that real estate gets its fair share of the country's investment-capital pool.

Here's what's happening:

The National Association of Realtors, working with two top financial-advisory firms, plans to create a huge "housing fund" that will go into head-to-head competition for the $550 billion now controlled by money market funds and other Wall Street mutual securities.

Virtually none of that $550 billion currently goes into housing--a fact that has frustrated home builders, realty brokers, labor unions and others eager to finance real estate.

The country's 264 money-market funds, for instance, control $231 billion in capital. Most of that amount is put into Treasury bills and short-term paper investments.

Money market funds have grown rapidly in recent years because of their liquidity and yield, often far higher than savers and small investors could obtain at banks or savings and loan associations.

One fund alone, for example, the American Association of Retired Persons' U.S. Government Money Market Trust, has grown from zero assets to over $4.5 billion in just two years.

Such money, say finance-industry sources, could be going into mortgage investments -- if a mortgage fund existed that provided similar liquidity and interest.

A publicly registered, professionally managed "housing fund" that could provide individuals and pension funds with a steady yield of 12 to 13 percent, they say, would be a smash hit. With a minimum investment as low as $1,000, the housing-market fund "could easily attract $500 million to $1 billion within its first 12 to 18 months of existence," according to one mortgage-finance expert.

A fund such as that is what's about to be launched.

The National Association of Realtors, along with the National Association of Home Builders, plan to "go public" with the idea once the federal Securities and Exchange Commission (SEC) reviews the concept and gives them the green light. That could take 60 days or many months.

Although certain details of the housing fund, such as its market name, are still up in the air, according to sources, the basic idea is firm:

The mutual fund will seek $50 million to $100 million to get rolling in the spring. A good chunk of this capital will probably come from the two associations' ranks.

The Realtors have approximately 650,000 members nationwide while the home builders have about 100,000. If just 200,000 of those members contributed $1,000 apiece to the fund, it would have $200 million to work with.

Heavy marketing campaigns targeted at real estate agents, builders, construction unions and housing industry-related firms are a key element in the strategy to build the "housing fund" quickly into a multibillion-dollar force.

The fund expects to put the money it raises into diversified pools of mortgage-backed securities. The securities themselves will be made up of conventional and government-insured loans. They will range from 16 percent, fixed-rate loans to below-market-rate, subsidized "buy-down" loans commonly used by builders to sell houses.

The sources of the securities will be the Federal National Mortgage Association (Fannie Mae), the Federal Home Loan Mortgage Corporation (Freddie Mac) and the Government National Mortgage Association (Ginnie Mae) as well as private mortgage-insurance firms, large banks and S&Ls.

A diversified portfolio made up of securities such as these would currently yield the fund about 13 percent, according to securities-market estimates. Investors in the fund could expect to net about 12 1/4 percent after the managers' and advisers' fees were subtracted. That compares well with the 9 percent returns available from money-market funds this week.

The key to the liquidity of the housing fund -- that is, its ability to pay out funds to investors on demand -- will be the diversity of its loan pools. No single mortgage security would get more than, say, 5 to 10 percent of the fund's total resources. That would allow the fund's investment advisers -- tentatively the large Boston firm of Thorndike, Doran, Paine & Lewis -- to liquidate holdings on terms favorable to the fund.

Management of the housing fund tentatively will be by the Philadelphia-based Vanguard Group. Vanguard manages 15 other mutual funds, with assets exceeding $15 billion.