Rep. Joseph M. McDade (R-Pa.), President Reagan's new point man for the forthcoming battle of the defense budget in the House, has more bad news for Defense Secretary Caspar W. Weinberger:

The defense budget can't keep growing as fast as it has.

"From the standpoint of the Defense Department and its credibility in the country, the deficit demands that the defense budget be part of the reduction process," McDade said as he prepared to take over as ranking minority member of the House Appropriations subcommittee on defense, a job that calls for him to defend the Pentagon money bill on the House floor.

McDade called for cuts in an interview conducted shortly after Weinberger met privately with the Scranton congressman to make his case for fighting significant reductions in the Defense Department's fiscal 1986 budget, which will go to Congress next month.

McDade's stand, together with the new call by Sen. Barry Goldwater (R-Ariz.), incoming chairman of the Senate Armed Services Committee, to freeze defense spending at this year's level, means that Weinberger will be fighting for his budget on at least three fronts: at the president's Office of Management and Budget, the House and the Senate.

"To try to get the old 14 percent increase or whatever this year in defense is just out of the question," McDade said, "and I intend to make that clear to the secretary."

Weinberger, who is in Europe, is scheduled to to return to his office Monday and plunge into the budget battle. Administration officials stressed that the big question is how much should be allocated for defense for Reagan's second term, not just the upcoming fiscal 1986 budget year. At stake, they said, is whether the president can reach his goal of getting the deficit down from $206 billion to $100 billion by fiscal 1988.

OMB Director David A. Stockman is recommending that the military budget be held below projections by $8 billion, $20 billion and $30 billion in fiscal 1986, 1987 and 1988.

McDade termed Weinberger "a committed individual, not an ideologue, who's trying to do his job, but there have been times when he has frustrated me terribly with his seeming unwillingness to recognize that we've got a tremendous deficit problem and that we have to treat the defense establishment as part of it.

"I don't know whether he would have come out better or worse" if Weinberger had been more flexible in his first four years, McDade said. "I can't read that tea leaf.

"But, from the standpoint of the Defense Department and its posture and its credibility in the country, it seems to me the deficit demands the defense budget be part of the reduction process."

McDade, a lawyer who will start his 12th term when he is sworn in next month, has been a staunch supporter of the Pentagon on most issues, including the MX intercontinental ballistic missile and the B1 bomber, and now is in position to build a Republican-Democratic coalition on the key defense appropriations subcommittee and on the House floor for Reagan's rearmament program.

He will succeed Rep. Jack Edwards (R-Ala.) as ranking subcommittee Republican. Edwards, who is retiring, led the successful fights on the House floor for the MX.

Rep. Joseph P. Addabbo (D-N.Y.), the subcommittee chairman who has repeatedly lost in his efforts to kill the MX and other pet Reagan programs such as the B1 bomber, said next year's session "will be the toughest one yet for the Pentagon." His subcommittee has one Democratic and two Republican vacancies to fill if the membership ratio is kept at 8 to 4.

Addabbo said the starting point for cutting the Pentagon's fiscal 1986 budget should be the amounts that Congress approved for fiscal 1985. Goldwater has called for freezing defense appropriations at the fiscal 1985 level.

In combating Addabbo and others on defense issues, McDade said he will employ Edwards' technique of listening to all points of view and trying to find the middle ground. He said he will try to save the MX by arguing that the president needs it as a bargaining chip in the new round of U.S.-Soviet arms discussions scheduled for next month in Geneva.

"It cuts the other way, too," McDade said of the MX. "You don't go all out when the talks are going on. You don't want to pull the plug on the program. The question of what one does about full production is another matter," he added in hinting that he will go for the middle ground of buying a few MX missiles in fiscal 1986 rather than going along with the Air Force request for $3.7 billion to continue research and to produce 48 missiles.

In contrast to his position on the MX, McDade is not in the administration's corner on covert aid to the "contras" fighting the Nicaragua government. He said any such aid should be out in the open and approved by Congress.

McDade also has a parochial side. He is known as "Mr. Coal" in some quarters of the Pentagon for insisting that the Defense Department buy coal in the United States to burn at defense facilities overseas. In fiscal 1984, foreign firms bought 270,000 metric tons of anthracite from McDade's home state for Pentagon buildings in Europe.

Asked if he considers himself a hawk or a dove, McDade, 53, replied: "How about an owl? I'm getting old enough to be an owl."