In a week of traveling around Europe, Caspar W. Weinberger, the new secretary of defense, left a trail of headlines and amiable confusion about his style of command.

He is, one-on-one, the most gracious defense secretary in recent memory and yet, in talking to a crowd, he can sound like the Cold War warrior since John Foster Dulles.

The 63-year-old Weinberger likes to start off his day with a gentle jog, dressed in olive drab coveralls. His morning run is billed as three miles, but it seemed much closer to half a mile the day he jogged along a gravel path in a Rome park.

Weinberger makes headlines easily. One day he indicated that selling arms to China was a real possibility. A few days later he dismissed the idea as "press speculation."

If he were not the nation's defense secretary and the closest thing to President Reagan's brother in the Cabinet, reporters could safely regard what Weinberger says as personal opinion subject to change without notice. But, under circumstances, it sometimes leads to confusion over how much or how little meaning lies in Weinberger's remarks.

But there was no misunderstanding his personal graciousness, especially with the staff people, like the secretaries who traveled in the back of the plane with the press.

It was almost a morning ritual for Weinberger to walk to the rear of the plane to ask his secretaries how they had slept the night before and whether they were eating well. At a formal reception in Bonn he broke off from the VIP's sought out his secretaries who had been trying to remain obscure, and told them about the history of the tapestries on the walls.

"In all the time I worked at the Pentagon," enthused one veteran secretary traveling with Weinberger, "I never even had anybody ask me if I had lunch. MR. Weinberger is so considerate. We just love him."

The Cold War Weinberger loomed large last Thursday morning when he spoke into the microphones before a crowd at the Rome airport. Although he spoke with his customary soft voice, the words were hard as he recalled the barbed fence separating East and West Germany that he had seen at Fulda, West Germany.

"I saw the prison wall, that great monument to Soviet realism, which stretches all the way from the Balkans to the Baltic," he said. "That prison wall was reinforced at great expense during the last few years -- the period in which we were engaged in the process called detente."

But back in the airplane, Weinberger stonewalled when reporters asked him to define the detente of the past and what detente would be like -- if it existed at all -- under Reagan. Are you against all kinds of U.S.-Soviet cooperative efforts? he was asked. Don't we have detent today under Reagan?

"I'm against unilateral disarmament," Weinberger replied, adding that he was against detente as it was practiced in the past. Beyond that he refused to elaborate.

The reporters brought up the question of whether the Reagan administration might sell arms to China if the Soviet invaded Poland. Weinberger told reporters on background -- meaning it could be used in press stories if it was not attributed to the defense secretary -- that "there's no linkage yet." At the request of the reporters, he allowed the remark to be put on the record -- meaning that now it could be directly attributed to him. His acting press secretary, in bringing the quote back to the rear of the plane, said the word "yet" should be underlined for journalistic purposes.

A few days later, however, Weinberger said selling arms to China was not under "active consideration," declaring the impression that it came from "press speculation."

Was it a chance remark? A trial balloon? A premeditated threat to Moscow carried by the press at a crucial moment of the Polish crisis? Only Weinberger knows for sure.

Pentagon aides traveling with Weinberger fit right in with his Cold War talk.

Undersecretary for policy Fred Ikle talked during the trip about the need to prepare for a Soviet "breakout," meaning the possibility of suddenly being confronted with a large number of offensive or defensive missiles. Arms control treaties limit launchers, not the number of missiles that may be stored in warehouses or caves. Worst-case advocates thus can conjure up threats from possibly thousands of hidden missiles.

Richard Perle, designated as assistant secretary of defense for international security policy and formerly chief architect of Sen. Henry M. Jackson's (D-Wash.) opposition to the SALT II arms treaty, stressed that the United States should not enter arms talks with the Soviets until it is ready, regardless of pleas from West Europeans.

Perle, incidentally, showed his customary self-assurance by buying a large clay pot in Rome and leaving it to the military people on Weinberger's plane to find a place to put it for the trans-Atlantic flight home. The pot ended up being strapped to a passenger seat in the rear compartment, then carried home from Andrews Air Force Base in the back of a military station wagon.

Weinberger's saber-rattling statements during the trip, no matter if they represented his own opinion or Reagan policy declarations, made more news than the carefully chosen words of Secretary of State Alexander M. Haig Jr., who was globe-trotting at the same time. In fact, for six days Weinberger outdid Haig in making news, prompting reporters to present the defense secretary with a black T-shirt adorned with white letters reading, on the front, "Haig & Haig 0," and on the back, "Cap the Shovel 6, I am in charge," with the "I" underlined to parody the fact that Haig had made the statement shortly after Reagan was shot.

"Now you've got to put it on and walk through the plane," a reporter told Weinberger as the Boeing 707, a former Air Force One during the Kennedy administration, whistled homeward from Europe.

Declining with a smile, Weinberger said, "There are limits."