A strong housing market is exciting for sellers and the real estate industry, but it can mean delays and screw-ups so bad that a sale falls through.

GMAC Mortgage has put together a list of common problems you may encounter when buying a house:- Unrealistic expectations. If you spend a lot of time looking at houses you really can't afford, you're bound to be disappointed. The best way to approach house-hunting is to go to a lender first with all your financial information. The lender can tell you precisely what you can afford and will promise to make you a loan for that amount if all your information pans out.

- Potential home buyers often fail to gather all the financial information needed to get a mortgage. Lenders want to know all about your money - your earnings, debts, obligations, cash assets, equities and sometimes taxes.

- If you are self-employed, you need even more documentation. GMAC says some borrowers don't even realize they fall into the self-employed category. "Ownership of 25 percent or more in a company or commissioned income means different documentation requirements."

- Credit problems can stop the home buying process cold. Especially nettlesome, GMAC says, are "credit explanations which are not adequately doc-u-mented and supported or which do not relate to the dates of delinquencies in the credit report."

- If your parents or someone else is giving you a gift to help with the down payment or closing cost, be aware that the lender will want to verify that the donor actually has the money to give and also to see how the money goes from donor to recipient.

If you have a fairly low income, a high mortgage interest rate and just a little equity in your house - at least 3 percent - you might be able to refinance through a pilot program announced recently by Fannie Mae. The idea is to help people who normally wouldn't qualify for a refinance reduce their monthly payments.

To qualify for the program, you have to work through one of these community or-gan-i-zations - ACORN Housing Corp., Community Mortgage Loan Pilot Initiative, Consumer Credit Counseling Service (800-388-2227), HomeChoice, National Council of La Raza, National Training and Information Center, Native American Con-ven-tion-al Lending Initiative, Neighborworks Product, and Neighborhood Infill and Stabilization Program.

If you can't find an office of any of these organizations in your local phone book, Fannie Mae can tell you if one is available in your area. Call toll-free 800-732-6643 and ask for HomePath Services.

If you buy a house and know it will need repair work right away, it's probably a good idea to get the home improvement money when you get the mortgage. Source One Mortgage (248-488-7000) is advertising a program that allows you to get a mortgage based on the value of the house after the improvements are complete. The loan program is called Renovation Plus. Other lenders in your area may be offering similar deals. It's worth checking out if you plan to buy a fixer-upper.

If you're debating whether to pay down your mortgage or invest in the stock market, consider these numbers, courtesy of the Institute of Certified Financial Planners: During the last three years, the S&P 500 Index returned an annual average of 33.4 percent. And large company stocks returned 15.3 percent annually from 1987 to 1996.

However, history tells us these lush numbers probably will wilt at some point. In the 1950s, for example, the average return on stocks was a satisfying 19.4 percent. But in the 1970s it was a paltry 5.9 percent.

The institute's advice: "Keep reasonable expectations."