A Pentagon estimate withheld from the public in the last days of the Ford administration put the most of the B-1 bomber at $112 million a copy instead of the advertised figure of $93 million, according to a General Accounting Office analysis released yesterday.

Sen. John C. Culver (D-Iowa) said in releasing the GAO summary that other data he has received actually pushes the price of the bomber up to $117 million.

The climbing cost estimates of the B-1 come as President Carter nears his decision on whether to put the bomber, the most expensive combat plane ever built, into full production.

He said during his election campaign that it would be "wasteful" to produce the bomber but lately has been showing signs of reversing himself.

Elmer B. Staats, head of the GAO, which serves as Congress' cost accountant, wrote Culver that his agency had been denied access to the higher Pentagon cost estimates until recently.

The GAO discovered that in addition to the Air Force cost report that then-Defense Secretary Donald H. Rumsfeld had accepted - that 244 B-1 bombers could be bought for $22.8 billion or $93 million each - there were two independent analyses casting doubts on the estimate.

Rumsfeld's own cost review team, Staats said, considered as "most reasonable" the analysis that argued $22.8 billion was 20 per cent below the most likely cost of developing and building 244 B-1 bombers.

Adding that 20 per cent increase, or $4.56 billion, raised the $22.8 billion estimate Rumsfeld publicized to $27.36 billion, or $112 million a plane.

Culver said yesterday that the Ford Administration "obviously" put out the lowest figure for fear of jeopardizing "this unnecessary and wasteful program."

Since Carter became President, the Pentagon has acknowledged that the B-1 is likely to cost $101.7 million a copy but has yet to endorse Culver's estimate of $117 million each.

Both the House and Senate have authorized the Air Force to spend $1.261 billion in Fiscal 1978 to produce five more B-1 bombers. Three were authorized last fiscal year.

Carter, if he does keep the B-1 in production, is expected to recommend building fewer than the 244 planes the Air Force wants.

Pentagon sources predict there will be a mixture of B-1 and older B-52 bombers until Carter assesses the prospects for reaching a strategic arms control agreement with the Soviets.

Lt. Gen. Alton D. Slay, Air Force research chief, said in recently released testimony before the Senate Armed Services Committee that although the B-1 would be harder than the B-52 to shoot down, "we have never said that it is going to be an easy task to shoot that B-52 down in 1985."