By 1986 the corporate sale of tax breaks under the new tax bill will reach $14.7 billion annually, according to Treasury projections. This will amount to more than $1 out of every $4 in the business tax reduction.

These tax estimates emerged at the Senate Finance Committee yesterday as Treasury officials reaffirmed their strong support of the paper transactions called "leases" under which companies buy and sell tax credits and deductions. They contended that the provision was essential to prevent a wave of tax-motivated mergers and to spread the benefits of the tax cut to corporations without tax liability.

At the same time, however, evidence of growing congressional hostility to the provision emerged both at the hearing and in a separate call by 16 freshmen Republicans for a major revision of administration fiscal policies, including "closing tax loopholes such as the so-called tax leasing provision."

While largely defending the corporate tax sale section of the $749 billion tax cut passed earlier this year, Finance Committee Chairman Robert Dole (R-Kan.) told the Treasury at the end of the hearing: "This provision is in some jeopardy."

The Treasury's estimates of new leasing revenue losses in 1986 are based on a combination of both the section of the law allowing corporations to enter into the new form of transactions, which really amount to tax sales, and the expected tax losses that would have resulted under increased traditional leasing activity because of the accelerated depreciation schedules.

Total revenue losses in 1986 from the business tax cut are expected to be $54.2 billion. Of this, $9.4 billion will result directly from the new leasing law, and another $5.3 billion would be prompted by the advantages created by the sharply increased value of depreciation.

John E. Chapoton, assistant Treasury secretary of tax policy, justified the leasing provisions on the following grounds:

* The provision does not create "extra deductions or tax credits." Instead, it allows firms that would be unable to use their credits and deductions from investments because they had no U.S. tax liability to take advatange of them by selling the credits and deductions to companies with tax liabilities.

* "Virtually all of the tax benefits . . . will be passed through to the company actually making the new investment." This claim has been disputed by other tax experts, who contend that, for the system to work, a significant portion of the tax benefit must be going to profitable, taxpaying firms.

* "Leasing does not guarantee a profit for bad investments; it merely provides the same tax investment incentives to firms without current taxable income provided to firms with taxable income."

Despite these contentions, many of the Democratic members of the panel who had strongly backed the Reagan administration's tax cut voiced strong opposition to the leasing provision.

Sen. David Boren, a conservative Oklahoma Democrat, noting the possiblity that the administration will seek increased taxes on telephone use other than excise taxes, said, "I will certainly support repeal of this kind of tax break before I support any tax on the American people . . . There are some of us who will be in outright warfare."

Sen. Harry Byrd (Ind-D-Va.) said he could understand the economic logic of the leasing provision but contended that it "has tended to poison the whole tax bill." Citing the prospect of growing federal deficits, Byrd asked "how far can we go?"

Sen. Steven Symms (R-Idaho) appeared to support the leasing provisions and was particularly critical of The Washington Post for publishing stories raising questions about legislation, sarcastically referring to the paper as a "bastion of objective thinking."

Symms, however, was one of the 16 freshmen Republicans signing the letter that criticized the leasing provision and called for closure of the tax "loophole."