County Executive James Lighthizer's plan for a two-day jolt of good news blew up today when his chief administrative aide quit and leaks spoiled his scheduled introduction Tuesday of a new police chief.

Lighthizer was to announce the first appointments of his new Anne Arundel County administration today--George F. Gisin as superintendent of the county jail and John Cecil as chief of inspections and permits.

But the appointments were upstaged when county administration director Robert Strott announced he would return to private industry. Strott oversees the budget, financing, personnel, purchasing, labor relations and other critical county functions.

His reappointment had been Lighthizer's first personnel decision and his departure was a shock, according to sources close to Lighthizer.

Strott, 50, said his decision was based on personal considerations and that he had no philosophical differences with the Lighthizer administration. "It was just time for me to make a career break," said Strott, who plans to join a Baltimore company.

Lighthizer also had scheduled a news conference Tuesday to introduce William S. Lindsey as new chief of the 450-member county police force, but the information was leaked by police sources and widely circulated.

Lighthizer acknowledged Lindsey's appointment by saying, "It's probably the worst-kept secret in American history." Asked why he didn't bring Lindsey to today's news conference, he said, "Obstinance, I guess."

Lighthizer said he always wondered why leaks of information worried presidents, but added with a chuckle, "Now I can empathize with Reagan."

He was less at ease with the loss of Strott. "Officially he's director of administration but as a practical matter he's much more than that," said the county executive. "He's been the top nonpolitical manager in Anne Arundel County for the last 11 years. As soon as I won the primary I called him to say I wanted him to stay on if I won the election.

"His leaving will make a tough job that much tougher," said Lighthizer, who faces immediate difficult decisions on increasing tax rates and utility rates to make up budget deficits. Strott has agreed to stay in the $58,000-a-year job until April 1.

Gisin, 41, chief of operations at Baltimore City Jail, will be the first independent county jail superintendent. Previously county police ran the jail. Gisin's appointment was recommended by a four-member advisory panel.

Cecil, 58, Lighthizer's choice for Inspections and Permits, is a former deputy secretary of the state Licensing and Regulation Department.

Lindsey, 50, whose appointment as police chief will be announced Tuesday, is deputy chief and a 23-year veteran of the county force.