WASHINGTON — Just as the U.S. economy is making progress despite Europe’s turmoil, here come two new threats.

A congressional panel is supposed to agree by Thanksgiving on a deficit-reduction package of at least $1.2 trillion. If it fails, federal spending would automatically be cut by that amount starting in 2013.

Congress may also let emergency unemployment aid and a Social Security tax cut expire at year’s end.

Either outcome could slow growth and spook markets.

Analysts are concerned, but most aren’t panicking.

Many say the economy and markets can withstand the blows. That’s because Congress or the Federal Reserve could take other steps next year to lift the economy. And investors expect so little from the congressional panel that they’re unlikely to overreact whatever it does.

“There’s no doomsday scenario in reducing government spending,” said David Kelly of JP Morgan Funds.

The 12-member bipartisan panel, or supercommittee, was created in August to defuse a political standoff over raising the federal borrowing limit. If it can’t agree on a deficit-reduction plan, automatic spending cuts would hit programs prized by both parties: social services such as Medicare for Democrats, defense for Republicans.

The panel appears to be deadlocked.

Economists say a stalemate makes it harder for Congress to extend the Social Security tax cut and unemployment benefits. On the other hand, if the supercommittee does forge a deal, it might include an extension of those benefits. Or it could at least clear the way for an extension later.

The Social Security tax cut gave most Americans an extra $1,000 to $2,000 this year. Unemployment benefits provide about $300 a week. Most of that money quickly and directly boosts consumer spending, which drives the economy.

By contrast, an expiration of those benefits could cut growth by about three-quarters of a percentage point, economists say. Throw in other cuts, like those passed in the August debt deal, and all told, federal budget policies could subtract 1.7 percentage points from growth in 2012, according to JPMorgan Chase and Moody’s Analytics.

Given the tepid economy, such a hit could be damaging.

“It would be very difficult for an economy that’s doing well to digest, let alone one that’s barely growing at potential,” said Ryan Sweet, an economist at Moody’s.

The economy grew at an annual rate of 2.5 percent in the July-September quarter. Some analysts fear it could fall below 2 percent next year, especially if the emergency unemployment benefits and Social Security tax cuts aren’t renewed.

The U.S. economy faces other threats, too — from persistently high unemployment to Europe’s spreading debt crisis, which could hasten a recession.

If the automatic spending cuts take effect, the defense budget could be cut by nearly $500 billion over nine years. Some contractors are nervous.