If the U.S. government were run by adults bent on problem-solving, Congress would have passed immigration reform by now.

[IMGCAP(1)]Instead, Republicans and Democrats constantly play political fútbol with the issue. In this game, everyone is losing.

The most obvious losers are 12 million illegal immigrants living in constant fear of deportation or family separation and subject to exploitation. But they aren’t the only ones.

Because Republicans and Democrats can’t agree on reform, thousands of foreign scientists and engineers leave the country after earning degrees here and have to wait years hoping to return — depriving this country of their talent and purchasing power.

Cities and states all over the country are burdened with education, health and police costs associated with illegal immigration. A reform law might provide them with federal impact aid — and reduce the flow of undocumented workers — but Congress won’t pass one.

On top of it all, the federal government looks incapable of managing one of its bedrock responsibilities — controlling the country’s borders.

Presidents of both parties look impotent, the immigration issue gets more fractious by the year and, increasingly, state and local politicians decide they have to (or want to) take over what’s plainly a federal responsibility.

Even as they battle each other, both parties are losing, too. By demanding ever harsher enforcement measures, Republicans are kicking away support from Latinos, the nation’s fastest-growing demographic group.

And Democrats, by insisting on “comprehensive” reform to appease liberal and Latino activists, are losing the chance to enact incremental changes that might build a consensus for full reform.

It appears increasingly likely that President Barack Obama will fail to enact any reform bill this year despite having an overwhelmingly Democratic Congress.

He repeatedly promised Latino voters in 2008 that he’d push for a comprehensive reform bill in his first year in office, including setting most illegal immigrants on a path to citizenship.

Instead, he put priority on health care, jobs and financial reform — and even announced on Air Force One that Congress probably lacked the “appetite” for immigration reform.

This failure — along with a rate of deportations as high as under President George W. Bush — has cost Obama support among Latinos while gaining him no credit among Republicans for stepped-up enforcement.

And what little chance of passing a bill there was this year may have been blown up by the Justice Department’s decision to sue Arizona for passing a law making illegal alien status a state crime.

The Obama case seems legally sound — no one would want New York, say, to enforce federal tax or environmental law — but it’s politically explosive, providing fodder for tea party activists and right-wing talk show hosts to denounce federal opposition to popular will.

Republicans were dug in before the lawsuit was filed, insisting that “securing the border” has to precede any other immigration reforms. They’ll be under even more pressure now.

In his immigration speech at American University last week, Obama asserted that “the southern border is more secure than at any time in the last 20 years,” and “we have more boots on the ground … than at any time in our history.”

The administration has a wealth of data to sustain the claim, but a recent Washington Post/ABC poll still showed that 75 percent of Americans don’t believe the government is doing enough to keep illegal immigrants out.

And Republicans are constantly raising their enforcement demands — including, building a fence across all 2,000 miles of the southern border. That would not stop 45 percent of all illegal immigrants who entered the country on legal visas, then overstayed.

Amid the toxic atmosphere, a few reform activists have decided to opt for something less than “comprehensive” reform this year.

Frank Sharry, former director of the National Immigration Forum and founder of America’s Voice, proposed last week that Congress pass just the DREAM Act and AgJOBS bill and work on comprehensive reform later.

The DREAM bill (Development, Relief and Education for Alien Minors), sponsored by Sens. Dick Durbin (D-Ill.) and Dick Lugar (R-Ind.), would grant legal status to about 1 million young people brought into the United States illegally as children if they are in college or join the military.

AgJOBS, sponsored by Sens. Dianne Feinstein (D-Calif.) and Lugar, would enable long-standing illegal farm workers — about 1 million, including family members — to gain legal status and would expand temporary worker slots for farm labor.

The idea of incremental reform has been advocated for years by the founder of the National Immigration Forum, Rick Swartz, but it has been resisted — and still is — by many activists who demand nothing less than earned legalization for most of the country’s 12 million illegal immigrants.

Swartz calls for passage of DREAM, AgJOBS, federal aid to states and localities affected by illegal immigration, “green cards for graduates,” expansion of high-skill H1-B visas and some enhanced enforcement as a “down payment” on more expansive reform.

A Swartz ally, Craig Regelbrugge, co-chairman of the Agriculture Coalition for Immigration Reform, told me that “you won’t secure the border without dealing with the economic migration piece, especially in agriculture.”

As many as 75 percent of U.S. farm laborers may be illegal immigrants and, in normal times, as many as 200,000 people a year enter the U.S. illegally to do farm work.

Immigration reform could provide a regulated entry for temporary labor. Without it, there’s every impetus for increasing imports of fruits and vegetables, costing jobs to American citizens in farm-related industries.

There’s a slim chance that the DREAM bill — possibly joined with AgJOBS — could come up for a vote in the Senate this year.

Some Democrats want to attach one or both bills as amendments to must-pass legislation this fall and dare Republicans to filibuster, risking charges that they are not only “anti-Hispanic,” but “anti-kid.”

Other Democrats don’t favor the ploy, however, fearing Republicans would seek to add harsh enforcement amendments.

Senate Majority Leader Harry Reid (D-Nev.) might try to block Republican amendments by resorting to a parliamentary tactic known as “filling the tree.”

A “down payment” bill ought to pass this year. After all, 11 Senate Republicans have supported immigration reform in the past. But the bottom line is that nothing at all will pass this year. What about next year?

Republican Conference Chairman Lamar Alexander (Tenn.) told me that 2011 should be the year for action both on the nation’s debt problem and immigration — but he said that “border security first” would continue to be the GOP mantra.

Obama, presumably, will want to push immigration reform hard next year, if only to repair his standing with Latinos who helped elect him in 2008.

You’d like to think that maybe Republicans and Democrats could act like adults, call a truce and agree to compromise reform legislation gradually leading to legal status for illegal immigrants.

You’d like to think it, but it would be utterly — and sadly — out of character for those in power in Washington, D.C.