OTTAWA — Worried that you've fallen behind in filing your federal income taxes?

Well, Ottawa has a lot bigger tax debt to worry about -- a whopping $18 billion in unpaid levies, says the federal auditor general.

And the size of the unpaid tax bill is rising at a much faster pace than the total taxes paid each year to the federal government, Sheila Fraser said in a report Tuesday.

If Ottawa made better use of its systems for tracking down tax dodgers, even a portion of that unpaid $18 billion could fund a lot of hospital beds, university research or new water and transit systems across the country.

"Any improvement in its ability to collect tax debts efficiently and within a reasonable length of time could add millions of dollars in revenues to the Crown every year,'' Fraser said.

Yet the Canada Revenue Agency can't seem to make good use of existing procedures for tracking and collecting back taxes, she said.

"The agency has known for many years what it needs to do to improve its collect of tax debts, but its efforts have fallen short,'' Fraser said after releasing her report.

Bills are unpaid on everything from personal and corporate income taxes to the goods and services levy, to payroll taxes collected by employers who then fail to remit them to Ottawa.

Despite some efforts by the agency to improve collections, the tax debt is outpacing total tax receipts.

The tax debt has grown by 88 per cent since 1997 while total taxes paid has grown 48 per cent, she noted.

Or, put another way, total tax debt as a percentage of tax collected sat a 4.27 per cent in 1996-97; by 2004-05, the proportion has risen to 5.43 per cent.

Many of Fraser's concerns mirror criticisms the auditor general raised 12 years ago in a previous study on the issue of outstanding tax debt.

And without dramatic changes to the way it operates, the agency will have a hard time improving its debt-collection record, she said.

In response, the agency said it has "agreed with (the auditor's) recommendations'' and is putting in place new plans to deal with the issues raised.

Fraser found the agency has more than 4,000 staff collecting on tax debts but still writes off a large chunk of uncollected taxes each year -- $2.7 billion was written off in 2004-05 alone.

Debtors may be insolvent, have no assets or have simply disappeared.

But an accumulated total of $18 billion in undisputed back taxes on 3.3 million accounts was still owing at the end of March 2005 -- about 45 per cent of that personal income taxes, she said.

And another $6 billion is outstanding but is in dispute by taxpayers challenging their assessments.