Continental Illinois National Bank, which may have bought as much as $200 million in bad loans from the failed Penn Square National Bank, yesterday fired one bank official and disciplined others following an internal investigation.

The giant Chicago bank cut back the authority of its top lending officer, who until last month was considered a leading candidate to be the bank's chairman within a few years, and fired John R. Lytle, 47, the officer in charge of energy lending in the Southwest who dealt directly with Penn Square.

Lytle had obtained a mortgage loan from Penn Square to buy a house in a Chicago suburb, according to officials of the failed Oklahoma City bank. A senior official at Continental said in an interview yesterday that Lytle's conduct "raised ethical questions."

Lytle later issued a statement charging that the bank was "trying to make me and the others scapegoats for the Penn Square debacle."

All told, the nation's biggest commercial lender made about a dozen personnel changes as a result of its six-week investigation of the Penn Square affair, and other actions may follow as the investigation continues. The results of that investigation are not expected until late fall or early winter, bank sources said.

"Our investigation has shown that strong measures must be taken to reinforce both the discipline and the management structure of Continental," said Roger E. Anderson, bank chairman.

Continental, the nation's sixth-largest bank, has followed an aggressive lending strategy that has left it with $1.3 billion in "nonperforming" loans that are not being repaid on schedule or involve other problems. It reported a $61 million net loss for the second quarter, largely because of the Penn Square collapse.

Executive Vice President George R. Baker, who is the bank's chief lending officer, was given a public "slap on the wrist," as a senior Continental official characterized it. He lost control over a division of 800 employes with the responsibility for servicing and documenting loans, including international and domestic business lending, made by Baker's subordinates. Baker retains control over most of the bank's lending.

Baker, 53, was considered a leading candidate to succeed Continental Chairman Roger Anderson, who will retire in a few years. Sources said the Penn Square fiasco would raise a serious barrier to Baker's advancement.

But the status of Gail M. Melick, executive vice-president for operations and management services, was enhanced by yesterday's shuffles. Melick had control over the servicing division until several years ago, when it was transferred to Baker in a "decentralization" move. Yesterday, Melick regained control over the division.

Along with Melick and Baker, the other chief contender for the top job at Continental, is executive Vice President David Taylor, who is the treasurer and chief funding officer. He was not involved in any of the Penn Square problems.

Continental bought more than $1 billion of loans originally made by Penn Square to oil and gas companies, mainly in Oklahoma and Texas. Other major banks -- including Chase Manhattan, Seattle First and Michigan National -- also were caught up in the Penn Square fiasco.

Chase, which reported a $16 million second-quarter loss because of the failure of its client Drysdale Government Securities Inc. in May, already has fired or demoted 10 officials for their role in Drsydale and Penn Square.

In addition to announcing the dismissal of Lytle, Continental disclosed the resignations of other officers. John A. Redding, who was head of the oil and gas group, retired yesterday and was succeeded by senior vice president Garry Scheuring, who has overseen Continental's loans to troubled International Harvester Co. Gerald Bergman, executive vice president in charge of the special industries department -- which controlled oil and gas lending -- left the bank. He was succeeded by John E. Porta.

Continental also accepted the resignation of the vice-president in charge of the group that directly lent money to Penn Square, and moved the bank's auditor to a new position. The head of the bank's loan administration division opted to retire.