President Reagan's plan for rearming America will cost at least $114.5 billion more than the one former president Carter had in mind, Pentagon officials acknowledged yesterday.

The Defense Department, in arriving at this figure, reported that the price tag for 44 major military programs, which was $340.3 billion last September, is now $454.8 billion.

Such a big difference is likely to intensify congressional concern that Reagan has bitten off more than the Pentagon can chew in ordering his record buildup of the U.S. military.

Sen. Sam Nunn (D-Ga.), an influential member of Congress in defense matters, already has said that the administration's strategy and the money available in future years to carry it out are out of sync.

Defense executives went to extraordinary lengths to explain the new increase, one larger than the projected deficit for next fiscal year, by holding briefings Friday and yesterday. The thrust of their comments was that the $114 billion rise is attributable largely to ordering larger quantities of aircraft, ships, tanks and missiles.

Lt. Gen. Kelly Burke, director of Air Force research, for example, said yesterday that the increase "is clearly part of rearming America." He stressed, however, that a relatively small slice of the $114 billion was attributable to avoidable cost overruns or poor management by the armed services.

According to the Pentagon, most of the $114 billion increase in the estimates of the cost of programs into the 1990s is attributable to larger orders for eight major weapons. They account for $99.9 billion of the total increase in the price tag between the end of September and Dec. 31, 1981.

Specifically, the 688 Class nuclear-powered submarine program is now estimated to jump from $14.6 billion to $24.3 billion, largely because Reagan intends to build 12 more of the subs than Carter had projected and will also put cruise missiles in their noses.

The Air Force's F15 fighter program is now expected to total $40.6 billion instead of the $25.2 billion buy Carter had in mind. Burke said yesterday that thanks to this additional money the Air Force will be able to buy 1,395 planes instead of 729. The production line is expected to keep going into the 1990s to fill that order.

Similarly, Burke said, the Air Force, under the Reagan program earmarking $40.9 billion for the F16 fighter instead of the $20.3 billion projected by Carter, will be able to buy 1,985 of these planes instead of 1,388.

In cruise missiles, in addition to the nuclear offense championed by Carter after he canceled the B1 bomber, which Reagan has revived, the Pentagon now figures the total buy will cost $8 billion instead of $6 billion. Again, the quantity to be purchased is larger: from 3,424 air-launched cruise missiles to 4,348.