The Pentagon may have to ask Congress for up to $20 billion more to cover the Persian Gulf buildup, The New York Times reported Monday.

The costs of the operation have risen sharply because of plans to add up to 200,000 troops to the U.S. forces already in the region, the newspaper said.U.S. officials said the request reflects an estimate that the Persian Gulf operation could cost as much as $31 billion, the Times said. It said contributions from American allies might offset less than half of that amount.

Despite the unknowns, such as what the precise cost will be and how much allies will contribute, a senior Pentagon official quoted by the Times said Congress may be asked to allot $16 billion to $20 billion more when lawmakers reassemble in January.

Before the Nov. 8 decision to add troops to those already in the Persian Gulf, it was estimated Congress would have to allot about $5 billion during the fiscal year that began Oct. 1.

The anticipated 1991 costs of the deployment will have no impact on the budget agreement struck last fall. The agreement omitted expenses for the gulf operation because they could not be calculated.

There was no immediate indication of whether the additional costs would be covered through higher taxes or through borrowing, the Times said.