Officials at American Airlines, fearing high mortgage rates might discourage key employes from relocating in this area, are ironing out the final details of a plan that will provide $50 million to $60 million in mortgage funds at 8 3/4 percent interest, substantially below the current market price.

The deal calls for American to purchase certificates of deposit from Republic National Bank of Dallas, First National Bank of Fort Worth and Continental National Bank, also of Fort Worth. The banks in turn will loan the money to Amercian employes for home mortgages.

American is relocating its corporate headquarters from New York to Dallas-Fort Worth. The company expects the move, involving 1,300 corporate level employes, to be completed by mid-year.

Officials at the airline said growing concerns that many middle-and upper-middle management people might not move to Dallas-fort Worth with the airline this year because of the high cost of purchasing a home spurred American to secure the financing with the three banks.

"The key point is that we regarded the unusually high interest rates as a temporary phenomenon, and we had many people being asked to relocate from homes in New York with loans in the 5 to 8 percent range," said Thomas G. Plaskett, American senior vice president of finance.

"It was one of the key factors bearing on our people's minds in their decision to reloacte," he added. "It was likely at the time that it would not have been economically attractive for our people to relocate. We did not want to get into a situation of losing a lot of our key people. It would not have been fair to our shareholders to gut the company of its key management people in order to move."

Plaskett said that while the company has been negotiating the deal for the last six to nine months, growing concerns among American emplyes became evident in December through a study conducted for the airline by Merrill Lynch Relocation Management Inc. The Merrill Lynch Co. is responsible for aidng American employes in their move to Dallas-Fort Worth.

Specifically, American has agreed to purchase the certificates at about 7 1/2 percent, a rate it has made off shortterm investments when interest rates have not been so high and a rate substantially below what the instruments usually bear at current interest rates. The savings the banks make in selling the certificates will be passed on to American employes when they take out mortgages on their homes.

While interest rates on certificates vary according to their maturity time and their denomination, current interest rates on three-year government bonds are 9.17 percent, and financial experts say rates on bank certificates would be slightly more. The amount the banks save in selling the certificates to American will offset the interest they would make if the money was loaned to other mortgage or commercial customers.

The plan calls for American employes to receive 80 percent home financing at 8 3/4 percent interest. Current mortgage interest rates in Texas are about 9 3/4 percent but can actually equall more than 10 percent when "points" of fees are added to the cost of the loan.

In addition, the deal guarantees that loan money will be available for American employes. Officials at savings and loans say Texas' mortgage ceiling of 10 percent is cutting off the supply of money available and forcing S&Ls to require higher down payments.

Plaskett said American would purchase the certificates from the banks on a monthly basis as airline employes take out mortgages. American most likely will buy the certificates with five-year maturities or less, he said.

In a time when mortgage interest rates are so high -- about 10.6 percent nationally -- and home financing funds in Texas are scarce, the American investment provides a source of mortgage business the banks might not have had. Additionally, the banks stand to gain the personal banking business of American employes.

Assuming that 800 of American's 1,300 employes moving to Dallas and Fort Worth buy homes in the $50,000 to $60,000 range, the airline will have to buy $40 million to $50 million in certificates. However, the average cost of homes is more likely to be $70,000, industry observerssay.

For the family buying a home, the difference in interest rates will mean a savings in the cost of purchasing a house of about $10,000.

And that savings translates into lower monthly mortgage payments.

Plaskett said the airline would be able to fund the purchase without retiring currently held certificates or other short-term instruments. He said the airline has $50 million to $60 million in short-term investments inaturing each month that could be used to fund the Dallas-Fort Worth certificate purchases.

The certificates purchases also could be funded by excess cash reserves, a commodity most major airlines have more of these days as a result in a boom in air travel.

In all, American currently has about $5 million invested in short-term instruments, Plaskett said.

The American executive stressed that the airline would not be moving any large single source of funds from one city, such as New York, where well-placed business and government leaders have been highly critical of the carrier's move to Texas.