Lawrence J. Korb, the Defense Department's manpower chief, yesterday proved that he can be his own man.

He refused to take the advice of Henry E. Catto Jr., Pentagon information chief, not to have breakfast with Pentagon reporters because negative news might result.

"I was told I couldn't come," Korb said yesterday of his conversation with Catto. Korb said Catto told him that if he appealed to Defense Secretary Caspar W. Weinberger Catto would recommend against a breakfast meeting.

Korb said he appealed to Weinberger through the secretary's military aide, and was told that he could go to the news breakfast after all.

Catto, who is stepping down this summer as assistant secretary for public affairs, defended the breakfast ban during the regular Pentagon news briefing last week. Said Catto:

"At some breakfast meetings recently people have spoken sometimes without perhaps full forethought of the impact of what they are going to say, and so I got to where I thought it would probably be better if I could talk people out of this for a while. The secretary went along with that idea. There is no across-the-board ban. We're going to review it on a case-by-case basis."

The breakfast remarks that gave Weinberger the most indigestion were those by Richard D. DeLauer, Pentagon research chief, that the Navy's Trident I submarine problems had shown itself to be seriously flawed in recent flight tests.

Adm. James D. Watkins, chief of naval operations, disputed DeLauer at a breakfast with the same group of reporters the next day, May 18. The admiral also said pointedly that Navy Secretary John F. Lehman Jr. should not be the one to decide whether aircraft carriers in a war should be sailed into the teeth of Soviet defenses. This would be up to operational commanders, the admiral huffed.

"I am unhappy when senior officials of the department become involved in saying things that they haven't perhaps thought out," said Catto. "The breakfast meeting has tended to bring out tongues in gear before minds are in gear."

Now that Korb has successfully appealed the breakfast ban, the question is whether Gen. E.C. Meyer, the Army chief of staff, who is retiring at the end of this month, will do likewise. The nation's top soldier is scheduled to have breakfast with Pentagon reporters, but has been advised by Catto to break the date.

"Armed forces people are supposed to be ready for attack at dawn," one reporter joked.