To San Antonio restaurateur Jerry Abel, signing a petition to abolish the federal income tax code after the year 2001 ranked among the easier decisions in the busy day of a small-business owner.

"What do we have to lose?" asked Abel, owner of Earl Abel's Restaurant. "Anything is better than what we've got."Abel and 750,000 other small-business owners have signed the scrap-the-code petitions, a campaign backed by the National Federation of Independent Business, which enjoys ample clout among GOP leaders.

The federation plans to display the petitions this week on the Washington Mall, Congress's back yard, urging congressional support for largely Republican-backed abolition legislation that would put in place a simplified system such as a flat tax or national sales tax.

The political and economic undercurrents of the scrap-the-tax-code effort are complex. The Clinton administration, along with some academics, fear it could disrupt the economy and businesses themselves.

And while business people like Abel express frustration with the unwieldy tax code, one study suggests the tax collector finds small businesses to be the most problematic of all taxpayers.

The Internal Revenue Service said 30 percent of individuals reporting business income aren't complying with the tax code. The 1996 IRS report, which examined who isn't paying taxes, cited a far lower noncompliance rate for individuals, about 2.5 percent.

"Taxing small business is always a problem, because you don't have anybody looking over their shoulder," said Bob McIntyre, tax policy specialist for the liberal Citizens for Tax Justice.

McIntyre draws a connection between this noncompliance and the small businesses' disdain for the IRS. "Because they cheat more, and they get into more disputes with the IRS, they dislike the IRS more," he said.

Donald Danner, the independent business foundation's vice president for federal relations, said while he can't confirm the study's estimate of noncompliance, he feels problems stem from the tax code's complexity, not willful tax evasion.

"It's no wonder that a lot of small businesses are not in compliance, because it's too complicated," Danner said.

Danner cited a 1996 Tax Foundation study that showed for every $100 they paid in income taxes, small businesses with net profits paid $377 in accounting fees and other costs to comply with tax laws.

His complaints draw support from University of Michigan professor Joel Slemrod, a leading tax expert. "The ratio of compliance costs to tax payments is much higher for small businesses," he said.

But Slemrod said it is "a really bad idea" for the federation to seek to abolish the tax code without identifying a replacement system.

"To say we get rid of it and not specify (the replacement) would be tremendously unsettling for the economy and unsettling for the businesses," Slemrod said.

Danner said bills to abolish contain a sort of safety valve: The tax code would be eliminated on Dec. 31, 2001, only if Congress has approved a replacement by July 4, 2001.

Less clear is how small businesses would fare under the flat tax or national sales tax.

Critics say a sales tax would transform businesses into tax collectors. Abel isn't concerned. "We're already that," he said, referring to collection of state sales taxes.

Under a flat tax, critics say small businesses would lose important deductions for interest and other expenses. But Slemrod and others suggest small businesses would benefit greatly through the simplified structure.

The abolition campaign also has political overtones. Some say it could further galvanize small business support for the GOP in this year's midterm elections.

"It's mainly to try to elect more Republicans to Congress," said McIntyre of Citizens for Tax Justice.

Danner disputed that.

"We are supporting people who are supporting the issues that our members tell us are important," Danner said. "The fact is that at the moment, more Republicans support those issues than Democrats."

Business advocacy groups typically back more Republicans than Democrats. The federation's pattern of campaign contributions are no exception.

In 1997, the group's campaign spending arm, the "NFIB/Save America's Free Enterprise Trust," reported four times as much in contributions to GOP House candidates as Democrat candidates. In the 1995-1996 campaign cycle, the ratio was 11-1 in donations to GOP House candidates.