Reports that Wall Street, which made millions of dollars securitizing mortgages in recent years, is becoming more wary of Alt-A by putting loans back to lenders or by bidding less for them could be an indication that default rates will worsen before they improve.

The problems in subprime mortgages started late last year when big investment banks started returning delinquent loans to lenders. Many of those lenders have since filed for bankruptcy protection.

“The credit markets were showering the mortgage market with capital, and now that’s just evaporating,” said Mark Zandi, chief economist at Moody’s Economy.com. “The capital markets are going to exacerbate the problem, seemingly.”

Until recently, mortgage companies had been able to sell loans to Wall Street banks and other investors for a premium that was big enough to cover their costs of making the loans and to make a tidy profit. The banks would then package the loans into pools to be sold as bonds to hedge funds, insurance companies and other investors.

“Now you are selling at par or lower in some instances,” said Thomas M. McCarthy, a managing director at Carlton Group, a real estate investment firm that brokers the sale of mortgages. “It really throws the business upside down.”

For American Home Mortgage, the lower prices investors are willing to pay for Alt-A loans will mean that the company will earn from 40 cents to 60 cents a share in the first quarter. Analysts had expected it to earn $1.06 a share, according to a survey by Bloomberg News.

Beginning in the second quarter, the company, which is structured as a real estate investment trust, will reduce the dividend for its common shares to 70 cents a share, down from $1.12 in the first quarter. The company also said it would write down $484 million in mortgage securities it owns because of the lower prices at which the bonds were now trading.