InterFirst Corp., the third-largest bank company in Texas, said yesterday it expects a record second-quarter loss of as much as $285 million because of soured oil and real estate loans, including an $80 million loan to a former director of the company's flagship bank in Dallas.

InterFirst, which owns InterFirst Bank of Dallas, said it will boost its reserve against loan losses for the quarter to as much as $365 million, up from $34 million a year ago.

It said it will suspend cash dividends on common stock "for the foreseeable future." The company said it could not predict when it would be profitable again.

The holding company said that a large part of the second-quarter loss stemmed from problems with an $80 million loan to Edwin L. Cox Jr., who was a director of InterFirst Bank until resigning June 13. The bank is renegotiating the loan.

Neither Cox nor officials at InterFirst could be reached for comment late yesterday.

InterFirst had total assets of $22.1 billion at the end of 1985, but on March 31, its assets had fallen to $19.8 billion.

In mid-May, the company reported a 10 percent drop in deposits from the end of 1985, to $15 billion. Several anaylsts surmised that much of the loss came from the withdrawal of "hot money" from Europe. Hot money refers to rate-sensitive deposits of $100,000 or more from companies, brokers or wealthy individuals who move their funds in and out of institutions with slight changes in interest rates in order to earn the greatest return.

The financial health of InterFirst, like that of banks throughout Texas and other oil-producing states, is being affected by a dramatic fall in oil and real estate prices in recent months.

Many Texas financial institutions, large and small, are major lenders to the oil and gas industry and to real estate developers, and will face heavy pressure because their customers will find it difficult to repay their loans on schedule.

A Texas banker for one of InterFirst's chief competitors said that InterFirst's stock has been rising recently despite the bank's troubles, leading to speculation that someone was trying to buy the bank company.

The banker, who asked that his name not be used, said that it is not unusual, given the Texas economy, for banks there to take big losses "and swallow the bad medicine." He said such action does not indicate that a bank company is about to fold or be forced by regulators to merge.

Staff researcher Bruce D. Walker contributed to this story.