Control Data Corp. has completed "a complex restructuring" that is intended to separate the ailing Minneapolis computer giant from its healthy Baltimore subsidiary, Commercial Credit Co., the company said yesterday.

Control Data spokesman Frank J. Ryan said that details of the change will not be unveiled until tomorrow, but said the plan "will put a wall" between the companies so that their credit ratings will remain separate in the minds of Wall Street investors.

The goal is to prevent the problems of Control Data, which is losing money and is in default on $380 million in loans, from spilling over to Commercial Credit, a financial services company that makes consumer loans, leases vehicles and sells insurance, Ryan said.

The restructuring will "redefine the legal relationship" between parent and subsidiary, but will not affect ownership, company officials said. Control Data will continue to hold 100 percent of Commercial Credit's stock.

Control Data, which is struggling to survive a computer-industry slump, defaulted on loans last fall when the Securities and Exchange Commission forced the company to restate its 1984 annual report. After the restatement, the company no longer met financial standards demanded by bankers.

The company said yesterday it soon will complete a plan to restructure its debt.

Control Data put Commercial Credit up for sale early last year but yanked it off the market six months later when it failed to get a satisfactory offer for the unit. Commercial Credit, which was profitable when Control Data bought it in 1968, has lost money for several years.

Its losses have slowed, however, and several Wall Street analysts say the unit is considered to be healthy.

Control Data had a record loss in 1985 of $562.7 million. Although Commercial Credit's operations were profitable last year, it ended up with a $4.8 million loss because of one-time write-offs. In 1984, the unit earned $48.6 million.