WASHINGTON — The American Taxpayer Relief Act of 2012, passed late Tuesday, addressed just one of three major issues that composed the cliff: the expiring Bush-era tax cuts. The government still faces jarring fights over the next two months, because it will need congressional approval to borrow more money and automatic spending cuts — delayed this week to allow more time to find alternatives — are scheduled to kick in.

Resolving the tax debate did buoy stock markets Wednesday, but shortly after they closed, the rating agency Standard & Poor’s warned that Washington didn’t accomplish enough to remove the threat of further downgrades on the creditworthiness of U.S. government debt.

“While congressional compromise designed to avoid the fiscal cliff may support the still-fragile U.S. economic rebound, the compromise doesn’t affect our view of the country’s credit outlook,” the agency said. “We believe yesterday’s agreement does little to place the U.S.’s medium-term public finances on a more sustainable footing.”

Similarly, Moody’s Investors Service said Wednesday that the deal amounted to just a “further step” in clarifying the deficit and debt trajectory.

“It does not, however, provide a basis for a meaningful improvement in the government’s debt ratios over the medium term,” Moody’s warned, making it clear that the United States remains on its negative watch list, where it’s been since September.

If Moody’s joins Standard & Poor’s in downgrading U.S. bond ratings, borrowing costs for the already heavily indebted government might rise sharply.

And if more than one rating agency takes away the AAA rating on U.S. debt, big pension funds and endowments that are required to hold only the safest of government bonds would have to shed their U.S. government bonds.

Simply put, there’s a lot at stake as the White House and Congress try to resolve their impasse on debt and deficits, which has stymied them for years.

The Treasury Department says the federal government hit its debt ceiling Monday, meaning that the agency is taking extraordinary measures to prevent default on payments already owed to creditors. Analysts suggest that those measures will run out somewhere between mid-February and mid-March, putting real urgency on coming talks to raise the debt ceiling before then.

And Tuesday’s deal punted on the automatic spending cuts due that were due to take effect this month, putting them off until March, the same month the federal government’s spending authority expires.

The two unresolved matters amount to two more major challenges involving federal spending and borrowing that threaten the economic well-being of ordinary Americans.

“The deal this week to avert the fiscal cliff provides some clarity to individuals and business decision-makers; however, the relief may be temporary,” John Silvia, the chief economist for Wells Fargo Securities in Charlotte, N.C., warned in a note to investors.

Lawmakers readily conceded that the agreement does virtually nothing to reduce the nation’s $16.4 trillion debt. In fact, the debt will continue to grow every year over the next decade.

“I hate this agreement. I hate it with every fiber of my being, because this is not the grand bargain that I hoped for,” said Senate Budget Committee Chairman Kent Conrad, D-N.D., who voted for the deal nevertheless. “This is not by any standard a deficit-reduction plan.”

Budget watchdogs were equally unimpressed.

“The main accomplishment of this bill was to make permanent most of the Bush tax cuts, and the Republicans seem to be ticked off about it and the Democrats are crowing about it. If you go back to 2007, this would have seemed like ‘Alice in Wonderland,’ ” said Robert Bixby, the executive director of the Concord Coalition, a budget-watchdog group. “If you see it as an attempt to deal with the long-term structural deficit, it’s a near-failure.”