The Air Force's B1 bomber program will cost $6 billion more for 100 aircraft than the Reagan administration originally stated, according to a congressional report.

Most of the $6 billion covers items purposely excluded from the original price tag of the strategic bomber by an administration eager to prove it could meet congressionally imposed spending limits. The General Accounting office, the investigative arm of Congress, said some of the cost increases also will be needed to correct major problems with the bomber's defensive avionics equipment and flight controls.

While the GAO report said the baseline, or basic costs of the B1, are expected to increase only slightly over the $20.5 billion ceiling set by Congress in 1981, it said the program will need to spend much of the $6 billion on maintenance, spare parts and flight training simulators that were not included as part of the base program.

"The point here is that the baseline number that everyone has focused on for years is a paper number that does not really reflect the true cost of what it will take to build 100 B1s and place them in the inventory," said House Armed Services Committee Chairman Les Aspin (D-Wis.), who requested the study.

However, an Air Force spokesman said, "The cost conclusions . . . are misleading. The B1 costs do not exceed expectations. The costs to acquire the weapons system, as well as support costs to deploy and operate the weapons system, have been programmed and included in all of the budget requests to the Congress."

Congress set strict spending limits on the program in 1981. Pentagon officials said they could remain within the budget. They did so by deleting many items from the original budget, saying they were unnecessary to the program.

Now the Air Force is planning to return to Congress and request that some of those items be funded outside the base costs, according to the GAO. The $20.5 billion 1981 ceiling is equivalent to about $28.3 billion in 1987 dollars, according to Pentagon estimates. The $6 billion cited by the GAO would be added to the program costs over the next several years.

Air Force officials said most of the costs outlined by the GAO report are "life-cycle" costs that were anticipated, but weren't included in the base budget. A spokesman said the Air Force in recent years has warned Congress the program will need additional money.

The GAO estimates that in addition to the almost $6.2 billion the program will need for flight simulators for training pilots, maintenance depot facilities and spares, it will need another $2.5 billion for improvements to the system.

Those improvements include upgrading its troubled defensive avionics equipment, incorporating new satellite communications systems, providing nuclear safety devices and accommodating classified weapons currently under development.

The GAO report noted that as of July 1, the Air Force has finished only 24 percent of the flight control testing for the B1, 64 percent of its testing for the troubled terrain-following radar system and had not started testing for most of the cruise missile system.