The nation's top military officer said yesterday that the armed services could easily spend whatever extra billions Congress might provide.

Air Force Gen. David C. Jones, chairman of the Joint Chiefs of Staff, told reporters at a breakfast session that anybody who says the military could not usefully spend another 5 percent a year "doesn't know what he is talking about."

Sen. Sam Nunn (D-Ga.) and others are demanding that President Carter increase the national defense budget by 4 percent to 5 percent a year, after allowing for inflation, to make the pending strategic arms limitation treaty an acceptable risk.

The Senate Budget Committee figures that increasing the defense budget by 5 percent annually, after allowing for inflation, would average out to more than $20 billion a year for each of the next five years.

Although some key White House and Pentagon executives, as well as the majority of the Senate Budget Committee and the House Defense Appropriations subcommittee, contend that 3 percent a year extra would be financial overkill, even for the Pentagon, Jones disputed them yesterday.

He said just "a lot of mundane things" would eat up extra billions, such as fixing up planes that cannt fly for want of spare parts, repairing tanks and ships, giving pilots more flying time and repairing buildings on military bases.

The glamor weapons, such as new strategic bombers and missiles, do not need the extra money, he said. Instead, the conventional forces are going begging, even though a non-nuclear war in the future is more likely than a nuclear war.

"There is no quick fix" to make the U.S-Soviet strategic balance tilt more favorably to the American side, Jones warned. Dumping a lot of extra money on top of that already earmarked for the new MX blockbuster strategic missile, for example, would only get it ready a few months earlier than scheduled, he said. The MX is expected to be operational in 1986.

As for buying a new strategic bomber to replace the B1, which President Carter canceled, Jones siad the joint chiefs are a year away from knowing what kind they would like to build.

But there is, he continued, "a great backlog of serious and valid needs" for improving conventional forces, especially since the Soviet Union for years invested far more heavily in them than did the United States.

"My greatest worry is continuing complacency" that will keep the United States from responding adequately to this Soviet military power. He said "the feeling we'll muddle through" without spending extra money on defense is still likely to prevail, despite the focus on the question during the current SALT II debate.

"I do not believe that a nuclear war is likely as far out as we can project," Jones said. "The more likely situation out in the 1980s is that the Soviets will continue to project their power" in key areas of the world, perhaps by using their own troops instead of continuing to rely on Cuban proxy forces.

If the United States is not willing to keep raising the defense budget to maintain forces able to deal with such Soviet threats, Jones said, "we will have to look at that strategy," which calls for responding to a full range of contingencies. "I hope we don't have to do that," Jones said in reference to phasing down American commitments to match military capabilities.

Jones and the other members of the joint chiefs are allied with Nunn in the current battle of the defense budget.The president considers Nunn's support of SALT II vital as he presses for Senate approval of the treaty.

Therefore, demands for hither defense spending cannot be ignored by the president. At a minimum, he is expected to ask Contress to vote enough extra money to increase defense spending by 3 percent annually after allowing for inflation.