In a three-year series of moves within the American Telephone & Telegraph Co. system, public relations division planner Frank French has gone from a 6.5 percent mortgage to an 8.5 percent mortgage to a 12 percent mortgage -- one of the reasons corporations say they are experiencing growing difficulties in relocating employes.

On the whole, French was happy about the move back to the Chicago area to work for Illinois Bell after a three-year rotation stint in AT&T's New York City offices. "The painful part of it is financial," said French. "I never thought I'd be happy to get a 12 percent mortgage."

Like many corporations, Illinois Bell is helping to ease that pain by paying a differential for five years between he mortgage rate French is leaving behind in Middletown, N.J., and the one he will assume in Flossmoor, Ill.

"We try to make a move so that an employe suffers no major economic losses," said Julian Dorf, AT&T's supervisor for employe relocation.

That chore has become more difficult as changes in the economy and in the way people live have combined to complicate the question of whether to move or not to move, according to a new survey on the subject.

He nationwide study of relocation policies of 603 major corporations sponsored by Merrill Lynch Relocation Management, a corporate relocation service firm, found employes refusing to relocate for a variety of reasons, including difficulties in finding jobs for spouses and concern about the high cost of living in the area to which they were being offered a job.

The survey found that changes involving a softened real estate market and an increase in mortgage interest rates caused increasing problems in disposing of employes' former homes and finding and financing new ones. Since 1978, the year which the survey covers, the real estate market has softened further and interest rates risen to record levels.

"I was in a meeting recently with representatives from about 30 companies, all saying 'what are you doing about mortgage money?'" said dorf. "I don't think there is a good answer to finding mortgage money. Employes just have to scramble."

Because of difficulties in the real estate market, the Bell System has asked employes in New York and New Jersey to postpone routine rotational moves for a year, if possible, said Dorf.

The Merrill Lynch study found corporations liberalizing benefits to offset some of the problems involved in relocation. Of the firms surveyed, 98 percent reimbursed employes for lease-termination penalties, 38 percent for rental finders fees and 34 percent for security deposits.

"The liberalization of relocation benefits to renters reflects the increasing number of employes who report difficulty in finding rental units in major metropolitan areas," said Weston E. Edwards, chairman of the Merrill Lynch relocation firm.

The survey also found that more than one-fourth of the firms reported difficulties in selling employes' homes because of problems that include the tight money market.

The two areas where selling was reported to be most difficult were the Middle Atlantic States, which includes the Washington area, and the North Central States. The Middle Atlantic was also the area in which finding rental housing for employes was considered the most difficult, according to the survey. Employes were reported most reluctant to transfer to the West Coast and into this area because of concerns about the high cost of living.

The study also found that the number of firms offering help in finding a job for an employe's spouse has doubled since a similar study a year ago.

Merrill Lynch also surveyed corporate attitudes toward refusal to transfer and found that 45 percent of the companies said it held no penalties. However, 8 percent of the companies said refusing a transfer could hinder an employe's advancement, and another 20 percent said refusal was permissible if the reason was valid.

"We don't punish people who don't go," said Dorf.