NEW YORK (CNNMoney.com) -- As thousands of illegal immigrants plan to rally Thursday in Washington, politicians, including President George Bush, have already stated their support of a guest worker program that would allow millions of foreign workers to find gainful - but temporary - employment in the United States.

But by law, guest worker programs already exist in the U.S. For example, an unlimited number of people can qualify for H2-A visas, intended for seasonal agricultural workers. Yet of the millions of undocumented field workers in the U.S. only 7,011 such visas were recorded as admissions by the Department of Homeland Security in 2005.

So few are issued because the vast majority of the millions of non-immigrant workers in that category can find work without the hassle of proper documentation.

"The temporary visa laws never worked to begin with," said Dan Kowalski, immigration lawyer and editor of Bender's Immigration Bulletin. Once the Immigration Reform and Control Act of 1986 became law, Kowalski explains, thousands of employers realized there was no category for their employees.

"They then didn't want to or didn't go to Congress to get visas. More likely it was cheaper to continue with an illegal work force."

And the business lobby has grown accustomed to the inexpensive labor.

University of Virginia economist Peter Rodriguez agrees, "We haven't had a full guest worker program of any kind. Instead we have an ad hoc system that manages job pressures."

Of all the failing worker-visa programs H1-B is the one that works best, although it's still rife with problems.

There is a cap of 65,000 new visas a year for skilled workers under the H1-B program, but exemptions and renewals up the true number to about 200,000.

From an economic perspective, the patch work of visas doesn't allow workers to be allocated to places where they're most needed, said Rodriguez. "Instead they go where the politics have allowed it."

Going to Congress is the only place for employers to ask for adjustments to the job categories covered by visas.

"All visas represent the historical needs of industries." Kowalski says.

In 1999, an obscure bill was passed that was tweaked specifically to allow accounting firms to transfer workers from abroad into the U.S. Kowalski struggled to understand the reasoning behind such a specific change in law.

He tracked down its legislative history and learned that when a big accounting firm needed to get some managers from Canada into the U.S. to work, it turned to a lobbyist on Capitol Hill who took it up with Congress.

The volatile nature of the 2006 mid-term elections makes the prospects of comprehensive immigration reform, including a provision for guest workers, hard to predict.

Currently, the Reid-Kennedy plan in the Senate would create a special guest worker program for an estimated 1.5 million immigrant farm workers, as well as provide 200,000 new temporary guest-worker visas a year. Also, demands in the labor market could raise the number of H1-B visas issued, which under the proposal would see its cap raised to 115,000.

The House's bill makes illegal immigrants felons and provides for no guest worker plan.

There's an alternative to the Democrat-sponsored Senate plan pushed by Republicans Rep. Mike Pence and Senator Kay Bailey Hutchinson, which aims to be a compromise between the House and Senate.

At the national level the GOP is keen to welcome the Latino vote as a source of future members. President Bush has been vocal since 2001 on the need for a guest worker program.

Unfortunately for GOP strategists, many congressional candidates this season see a crackdown on illegal immigration as a way to motivate Republican voters to get to the polls, which sends a chill through the same community the GOP is trying to court.

The conflict within the GOP has the majority party breaking Ronald Reagan's so-called 11th commandment. "Thou shalt not speak ill of a fellow Republican."

Rep. Tom Tancredo, for example, has established a political action committee to "secure our borders" and on its web site runs a column called 'Pence Watch,' aimed at Republican Rep. Mike Pence's immigration compromise proposal.

"No matter what happens [in the 2006 election] the White House will work with congress next year," said Brian Darling of the conservative Heritage Foundation.

But if the Republicans retain control, there will likely be more gridlock, Darling predicts.

Even if the Democrats win control of Congress, a guest worker program isn't guaranteed, according to Brian Friel from National Journal.

Rep. Nancy Pelosi, who would become the House Majority leader if the Democrats win, supports the provisions in the Senate bill too.

But even then divisions remain among the Democratic rank and file. The Congressional Black Caucus is concerned about how some of their lower-wage earning constituents would fare, and the AFL-CIO opposes the guest worker program as a path to second class citizenship.

Some Latino community leaders see the illegal immigration debate, in some ways, as a referendum on Latino political power.

Looking forward to 2008, if the issue remains unresolved or only partially resolved, DC-based immigration specialist Paul Donnelly predicts it "[Could be] a decisive values issue in 2008."

"There's a huge advantage for a Democrat for talking bluntly about why our immigration policy is broken."

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