Oct 30 (Reuters) - The U.S. Treasury Department is expected to increase auction sizes when it announces its quarterly refunding next week and continue shifting more of its debt into longer-term obligations. The Treasury has been boosting the size of its debt sales across the curve to pay for a rapidly expanding government deficit. The prospect of more spending to boost the economy once the result of next week’s presidential election is known could add to its financing need and the Treasury may signal a larger jump in issuance in 2021. Even without new fiscal stimulus the government is still expected to push more of its debt into the longer-end of the Treasury curve, after relying heavily on Treasury bills to finance a record $2 trillion of stimulus in the second quarter of this year. “The deficit for this year has been huge and I think that they want to continue terming out debt and relying less on T bills outstanding, which have more than doubled in 2020,” said Zachary Griffiths, an interest rate strategist at Wells Fargo in Charlotte. A wildcard for U.S. debt issuance in the next few quarters will be who wins the election, and how much fiscal spending they can get through Congress. Republicans and Democrats have both voiced support for a fiscal boost to an economy battered by business shutdowns during the pandemic, though there are large differences in the size of any potential package. A victory by Democrat challenger Joe Biden would likely spur spending of $2 trillion or more, especially if Democrats win control of the U.S. senate. Other initiatives including climate infrastructure would add to the bill. U.S. President Donald Trump also favors a relatively large package, though Senate Republicans have opposed going much above $1 trillion. The Treasury’s $1.7 trillion cash balance gives the government some room to pay for new spending without launching another deluge of bill issuance, “unless a Blue Wave brings even higher deficits,” said analysts at TD Securities. In either case “the likelihood of further fiscal stimulus after the election suggests that Treasury will need to keep preparing for larger deficits in the years to come by continuing to increase auction sizes,” they said. The weighted-average maturity of the Treasury’s outstanding debt is now 63 months, seven months shorter than average levels in the five years leading up to the pandemic, analysts at JPMorgan said. (Reporting by Karen Brettell in New York; Editing by Alden Bentley, Kirsten Donovan)