Add the Mortgage Bankers Association to those who are worried about homeowners taking out home loans that feature low initial payments that can rise dramatically over time.

But wait. Aren't the mortgage bankers the very people selling such loans? The answer is yes, but the MBA says the primary responsibility for being prudent in taking on debt rests with the consumer.

"Borrowers need to be vigilant to be sure that they are prudently measuring and managing" the added risks many accept by embracing loans that minimize monthly payments in the early years but can require much-higher payments later, the trade group said in a 30-page report.

The report echoes warnings from Federal Reserve Chairman Alan Greenspan, bank regulators and the National Association of Realtors about the risks of non-traditional loans.

The worrisome mortgages include interest-only loans with rates that follow prevailing interest rates. With these loans, borrowers pay only the interest during the first few years but then monthly payments rise sharply as the borrower begins paying off the principal.

If interest rates rise sharply over the next few years, many homebuyers could be in trouble, as their monthly payment could rise dratically as they try to cover higher interest rates as they begin paying on the principal.

Many buyers taking out such loans are counting on continued double-digit increases in housing values, perhaps thinking that they will be able to refinance or sell their home before the higher payments come due. That's not likely to be the case if the run-up in housing prices turns out to be a "bubble."

However, it's not just over-extended consumers that has the mortgage bankers group wringing its hands. Its report warns that "investor activity," meaning speculation, has increased in the hottest U.S. housing markets, primarily those on the East and West Coasts.

"Lenders need to prudently monitor the level of speculative activity in such markets," the MBA report cautioned. Speculation is a factor in driving up housing prices to unsustainable levels. Also, speculators are quicker to walk away from investments gone bad than owner-occupants.