Defense Secretary Frank C. Carlucci became a millionaire in private business during the four years between leaving the Pentagon's No. 2 position in 1983 and returning to government employment earlier this year, according to his federal financial disclosure reports.

Carlucci's disclosure papers, filed after he was nominated defense secretary in November, state that his salary and bonuses totaled $1.2 million in 1986, including a $735,722 "termination settlement" when he resigned as chairman of Sears World Trade Inc. -- which went out of business following heavy losses -- to become President Reagan's national security adviser earlier this year.

As a member of Reagan's Cabinet, Carlucci is being paid $80,100 per year.

Carlucci's salary in 1986 as a Sears executive was $385,794, according to the report. In addition, he was paid $63,000 in directors' fees and other compensation from six other corporations including UNISYS Corp., a computer firm that does business with the Pentagon; Rand Corp., and the American Stock Exchange.

The report also shows that Carlucci's investment and stock assets for 1986 and 1987 are worth between $1.1 million and $2.6 million, a sharp contrast to the assets he listed in a 1982 report, while he was at the Pentagon, that showed assets of between $30,000 and $100,000. Precise figures are not available because the federal reports only show a general range of values.

Carlucci, 57, earned between $72,000 and $201,200 from those investments during 1986 and 1987, according to the report. The records he filed in 1982 showed income from his assets as $1,900 to $11,500.

The defense secretary listed his only liability as a mortgage of $50,000 to $100,000 on a McLean rental property.

The four years as a top executive of Sears, Roebuck and Co. were Carlucci's only stint in the private sector after a long career of almost exclusive government service.

He was a foreign service officer early in his career, then was ambassador to Portugal. His resume includes a long list of administrative jobs: the second-ranking position at the Office of Economic Opportunity, No. 2 job at the Office of Management and Budget, second in command for the Central Intelligence Agency under Stansfield Turner and deputy defense secretary under Caspar W. Weinberger from 1981 to 1983.

He left Sears in December 1986 to become Reagan's national security adviser, replacing Rear Adm. John M. Poindexter. Carlucci succeeded Weinberger last month.