The Central Intelligence Agency and Defense Intelligence Agency are apart by a factor of four in estimating by how much Soviet spending on military hardware increased between 1982 and 1983, the Defense Department acknowledged at an unusual news briefing yesterday.

CIA officials, who could not be identified under ground rules of the briefing, estimated the jump at no more than 2 percent in dollars while their DIA counterparts projected an increase of 5 percent to 8 percent in the Soviets' military procurement account after inflation.

The CIA report that the Soviets have been in a period of "stagnation" in buying tanks, guns, ships and missiles comes at the time that Congress is looking for places to cut President Reagan's new defense budget, which calls for a 10 percent increase in procurement.

CIA and DIA officials stressed that the Soviets' procurement budget has gotten so big that a few percentage points more or less do not change the threat. But they gave no specifics on why their projections were so far apart.

The differences became public last week after a subcommittee of the Joint Economic Committee of Congress released the Nov. 21 testimony of Robert Gates, CIA deputy director for intelligence. Gates said, "The stagnation in the level of procurement lasted for at least seven years, from 1977 to 1983 . . . . The Soviet leadership in the mid-1970s may have viewed the external threat as manageable and the existing high level of procurement as enough . . . ."

As reporters filed into the office of Pentagon spokesman Michael I. Burch yesterday, they were handed a statement from Gates, who was not present, that it was "not correct" to portray his November testimony as "a major split between CIA and the Department of Defense on the Soviet military effort." Gates said that "what the Soviets actually have bought, are deploying and are developing" is far more meaningful than "an artificial reconstruction of what it cost them . . . ."

"The awesome fact is," Gates continued, "that despite a temporary leveling-off in the rate of growth in Soviet military procurement, the Soviets consistently not only outspent the U.S. throughout, but produced far more missiles, planes, warships, tanks and other weapons than the U.S . . . ."

Gates said the Soviet Union has been allocating between 13 and 14 percent of its gross national product to defense since 1965. This compares with 6.4 percent of the U.S. GNP that went to the Pentagon in 1985. The Soviet GNP is considerably smaller than that of the United States. The CIA in its 1984 World Fact Book figured the Soviet GNP as $1.7 trillion in 1982. The U.S. GNP that year was $3.1 trillion.

Members of the Joint Economic Committee have questioned why the Soviets are obtaining more weapons for a given amount of money than the Pentagon. One answer defense officials have given in the past is that it has been U.S. policy to overcome Soviet quantity with quality, which is a costly approach.

During the briefing, CIA officials projected that Soviet spending on weaponry would increased 1 percent to 2 percent in dollars between 1982 and 1983 and 2 percent to 3 percent in rubles. They declined to make projections for the jump in Soviet military procurement between 1983 and 1984.

DIA officials projected a dollar increase in Soviet procurement of 5 percent to 8 percent between 1982 and 1983 and predicted the rate of growth, after allowing for inflation, would be "similar" between 1983 and 1984.