National security adviser Frank C. Carlucci, 57, has made a lifelong practice of being the right man in the right place at the right time. Yesterday, it happened again when President Reagan turned to him to succeed Caspar W. Weinberger as secretary of defense.

The grandson of an immigrant Italian stonecutter, Carlucci rose from the ranks of the Foreign Service to play an important role in four administrations. In his new post, assuming he is confirmed by the Senate, he will step out of the shadows of the national security bureaucracy to center stage at the Pentagon.

Only last January, he was recruited from private industry to serve as Reagan's fifth national security adviser. Confronted with the job of rebuilding a National Security Council staff that was demoralized and discredited by the Iran-contra affair, he moved quickly to reorganize the operation and abolish its discredited political-military section, which Lt. Col. Oliver L. North had used for his covert escapades.

Carlucci also struck a note of symbolic difference with his predecessor, John M. Poindexter, by leaving open the door to his office, a sign that he welcomed discussions with other administration officials. A Reagan aide of the time praised Carlucci for ending the idea that there were two centers of White House gravity: "NSC and non-NSC."

In less than a year on the job Carlucci gained a reputation for smoothing conflicts within the administration, where feuds between the State Department and the Pentagon had been a persistent feature of the Reagan presidency. "I give Frank very high marks," said Rep. Dick Cheney (R-Wyo.), a House leader who once served as President Gerald R. Ford's chief of staff. "He's steered the administration between the rocks and shoals of State and Defense and won a lot of respect in the process."

He also won respect from a Congress that had learned to distrust the NSC and its proclivity for covert actions. A Senate aide who has dealt with Carlucci on a number of foreign policy issues said he was "a lot more savvy about the way Washington works" than his predecessor.

When the White House needed to find a compromise recently on an arms sale package for Saudi Arabia, it was Carlucci who handled the negotiations. "They {senators} were impressed with the way he handled it," said another Senate staff aide. "He came across as eminently reasonable."

Soon after he came to the NSC, Carlucci told a reporter that he valued both "politics and the bureaucracy and their interaction."

This comment reflected experience gained in three decades of public service. His Princeton wrestling classmate Donald Rumsfeld persuaded Carlucci to take over the community action programs of the embattled "War on Poverty" during the Nixon administration, and his performance won praise from Democrats and Republicans alike.

In this role, Carlucci was No. 2 man at the Office of Economic Opportunity. Later, he was No. 2 man to Weinberger at the Office of Management and Budget, No. 2 to Stansfield Turner in the Central Intelligence Agency during the Carter administration, and from 1981 to 1982, he served again as Weinberger's No. 2, this time at the Pentagon.

The only time Carlucci was No. 1 before his national security appointment was when he was ambassador to Portugal during the Ford administration. Then he sided with a minority of U.S. policymakers who wanted to continue economic aid to Portugal in the belief that it could be rescued from a drift to communism and become a stable democracy.

Carlucci's long travels through the bureaucracy to a top position in the Reagan cabinet had their perilous moments. The most dangerous of these came in 1960 when, as a young Foreign Service officer in what was then the Belgian Congo, he came to the aid of a carload of Americans besieged by an angry mob after a traffic accident in which a Congolese was killed.

Carlucci rescued the Americans but was stabbed in the neck in the process. His bravery and resourcefulness won the respect of future Congolese leaders and two years later brought him to the attention of President John F. Kennedy.

In private life, Carlucci was a relentless physical fitness enthusiast who rarely let crises interfere with a mile of swimming a day, frequent jogging and a highly competitive tennis game.

Carlucci was always friendly to reporters, but he was a tight-lipped master of the "no comment" when it served his purpose. Last night, at a dinner of the Council on Foreign Relations in New York, Carlucci was asked by a reporter whether he was the new secretary of defense. "No comment," he said, but the smile gave him away.