In the aftermath of a housing crisis built on easy credit, today’s tighter credit standards are widely accepted. But just how fine a comb lenders put to loan applications can be surprising.

California Realtor Scott G. Harrison tells the story of a recent buyer with a pending contract on a Bay Area condominium. Months earlier, the buyer had disputed a $15 charge on his credit card bill. Before the lender would approve the loan, the buyer would have to submit a written explanation. The issue was minor, but took 10 days to resolve.

“The littlest things can affect your financing, and buyers aren’t always willing or able to meet the demands,” said Harrison.

The sharp decline of home prices combined with low interest rates on mortgages have created a period of great affordability in the housing market. But in the aftermath of a foreclosure crisis predicated by a period of easy credit, banks have instituted tough lending standards that have made getting a home loan exceptionally difficult. With interest rates likely to rise later this year, millions of Americans remain locked out of the market for the foreseeable future.

“The trend is to offer credit to the cream of the crop,” said Walter Molony, a spokesman for the National Association of Realtors. “The pendulum has swung from crazy lax standards to overly restrictive standards that are denying seemingly credit-worthy borrowers.”

The decline in home prices since the bust of the housing bubble has been dramatic. In March of 2007, median price for existing home sales was nearly $220,000, according to the National Association of Realtors. By this March, median prices had dropped over 25% to just under $160,000. The Federal Reserve’s efforts to stimulate the economy by keeping interest rates down pushed average rates on 30-year fixed-rate mortgages to 4.84% from 6.16%.

In spite of great affordability, home sales have been sluggish. A shadow market of looming foreclosures has likely kept potential buyers on the sidelines, waiting for lower prices in months to come, and debts accrued during the economy’s boom years have left many in poor condition to take on new obligations.

But there is little question that tighter credit standards have kept Americans out of the housing market. A Federal Reserve study found that denial rates on pre-approved mortgages rose to 32.3% from 26.2% after new pricing rules took effect in 2009, and Freddie Mac reported its average FICO credit score for private mortgages as 752 in the first quarter, up from 707 in 2007. While the Fed reported that mortgage debt rose slightly over the last three months, tight credit is likely to slow home sales moving forward.

“The wet blanket in the intermediate term is going to be higher credit standards and the large percentage of people with credit problems,” said Russell T. Price, senior economist at Ameriprise Financial.

Now comes the likelihood that interest rates on long-term mortgages will rise in the near future. Last month the Fed indicated that it would end the $600 billion bond-purchasing program commonly known as QE2 as scheduled in June, and rising long-term interest rates are likely to result.

Fixed-rate mortgages tend to track the yields on 10-year Treasury bonds, explained Bernard Baumohl, chief economist at the Economic Outlook Group.

“If the Federal Reserve is not buying treasury securities, you would expect yields to go up,” Baumohl said. “If you figure that Japan is not going to be buying treasuries as it rebuilds after the earthquake, that would be two major buyers not buying treasuries.

Baumohl, however, argued that the effect on home affordability was hard to predict, suggesting that in a weak economy private investors might create a new demand for treasury bonds, pushing yields and long-term mortgage rates back down.

In a strong economy, rising mortgage rates could be offset by lower home prices, said Scott J. Brown, Chief Economist for Raymond James and Associates.

“If the economic outlook improves and interest rates rise, that might dampen housing demand, and you could expect prices to fall,” Brown said.

In the meantime, high standards and intense scrutiny remain barriers in a sluggish but highly affordable market.

“You have to get them ready for the frustrations and requests for more documentation from lenders,” said Harrison. “If they’re not prepared, the give up.