The $85 billion in cuts would impose "self-inflicted wounds to the recovery and put far too many jobs and businesses at risk," Lew said in prepared remarks Wednesday to the Senate Finance Committee.
The committee is considering Lew's nomination to succeed Timothy Geithner, who stepped down last month as Treasury secretary. Lew, who most recently served as Obama's chief of staff, is expected to win Senate confirmation late this month.
Helping to resolve a dispute between the White House and Congress over the proposed cuts to both defence and domestic spending programs would be his first challenge in office. But many others await him. He also would have to manage tense relations with China, press Europe to reduce debts while fighting a recession and defend the financial overhaul law.
Still, the job isn't quite as perilous as the one that greeted Geithner, who had to help stabilize the U.S. banking system after the worst financial crisis since the 1930s and help lift the economy out of the Great Recession.
The economy and banking system are far healthier now. Still, Lew will likely have to marshal all his strengths as a budget specialist and perhaps overcome inexperience in some areas to achieve significant success.
Lew, 57, is well-prepared for questions about taxes and spending. He has twice served as a White House budget director — once during the Clinton administration and once under Obama before becoming his chief of staff.
Going back to his days as an aide to House Speaker Tip O'Neill in the early 1980s, Lew has amassed three decades of experience at the top levels of Washington policy-making.
He isn't expected to have trouble winning Senate confirmation, despite the likely arguments from Republicans that the administration isn't doing enough to contain "entitlement" programs such as Medicare, Medicaid and Social Security whose costs are straining the federal budget.
After Wednesday's hearing, committee members will have two days to send questions to Lew to answer before they vote. The full Senate could vote on the nomination late this month.
That would give Lew little time before his first budget challenge — the March 1 date when deep spending cuts in defence and domestic programs will kick in unless Congress and the administration agree on some way to avert them.