The District's system of collecting income taxes from its residents includes a series of built-in alarms to locate those who fail to file returns but is sometimes hampered by the sheer volume of cases and the transient nature of Washington's population, according to several experts.

Most of 300,000 District residents who annually file city tax returns do so on time, but when they do not, officials in the D.C. Department of Finance and Revenue have a number of discovery and collection techniques at their disposal, ranging from mild letters of warning to property seizures for the worst offenders.

The case of Eleanor Holmes Norton, the Democratic candidate for D.C. delegate to Congress who failed to file city taxes for seven years, has thrust the tax-collection arm of city government and the department's procedures into a rare spotlight, with most experts agreeing that District officials had the means at least to detect her failure to file.

After the disclosure two weeks ago that Norton, a law professor and former Carter administration official, and her husband, Edward, had failed to file city tax returns since 1983, Eleanor Norton paid the D.C. treasury more than $28,500 in back taxes and penalties. Today, she is expected to announce another large tax payment to the city and disclose her local and federal tax documents for the seven-year period.

One of the main tripwires the D.C. government uses to find residents who do not pay local taxes is a computerized cross-check with federal tax filings. Every October, according to an IRS spokesman, the U.S. government provides the city with a computer tape listing the names of people with District addresses who filed a federal tax return in the previous year.

The District can then match those names with a list of District tax filers and come up with a list of potential non-filers.

One former official of the D.C. Department of Finance and Revenue, the city's tax collection agency, said that once residents file a return with the federal government and "they put a District address on it, the odds are the District would catch it . . . . You can bet on it."

The cross-check is not foolproof, however. There are hundreds of people living in the District who are exempt from local taxes, including members of Congress, Supreme Court justices and certain congressional staff members. But according to former city officials familiar with the program, the federal match should catch most of those who should file but do not.

Eleanor Norton has said that she and her husband filed their federal tax returns year in and year out, and attributed their failure to file locally to a number of factors, including Edward Norton's "procrastination" in a long-standing tax dispute with the D.C. government. She also has said that although her husband alone handled the family's tax matters, the responsibility for ensuring that local returns were filed was equally hers.

Officials with the Finance and Revenue Department have said they are investigating the circumstances behind the Nortons' failure to file D.C. tax returns as they would disclosures about any other taxpayers.

At the same time, department officials said their strict rules about taxpayer confidentiality prevent them from discussing the Norton case specifically. "This is not being treated differently than any other case," said department spokesman Linda Grant.

Grant said she could not comment on whether the system worked or failed in the Nortons' case -- leaving unanswered the question of whether the Nortons' case simply fell through the bureaucratic cracks of the D.C. government, or conversely, that the city knew of the problem, diligently tried to collect money from the Nortons, and until recently was unsuccessful.

According to tax accountants and lawyers familiar with the District's procedures for catching tax scofflaws, a number of people fail to file every year, but then go undetected by the city's tax collecting agency. Bureaucratic slip-ups common to most state tax collecting agencies were cited as the major reason why some of those who do not pay are not discovered.

"I'm not suggesting it is right, but it happens," said Jeffrey P. Capron, a lawyer and accountant who represents D.C. taxpayers. "It is not terribly uncommon. I've known people who have lived in the District and filed federal returns and not D.C. returns. Years go by.

"It is not sensible, and ultimately you're going to get caught," he said.

In instances of failure to file, the city's typical practice is to send out a non-threatening letter informing the person that city records indicate that the taxpayer has not filed the necessary tax returns, former officials said. Often, that simple nudge works.

Grant said that in the past two years the city has sent out about 25,000 notices of failure to file resulting in 12,000 people filing their returns in response. The District also has the power to attach liens against residents' houses or bank accounts if they don't respond or to refer the case to the Corporation Counsel's Office for prosecution.

Failure to file is a misdemeanor, which depending on the circumstances is subject to a fine of up to $5,000 and one year in jail. But officials of the Corporation Counsel's Office say they typically don't prosecute such cases, preferring to work administratively with the Department of Finance and Revenue to recover any money owed the District government.

"We haven't filed a criminal case in a number of years," said Claude Bailey, a spokesman for the office. "We want the money, and the criminal cases usually don't interest us."

Because both Nortons are lawyers, their conduct also can be scrutinized by the District's lawyer disciplinary machinery.

Bar Counsel Thomas Flynn, who cautioned that he was speaking generally, said, "Mere failure to file would not necessarily be a violation of the code . . . but depending upon the circumstances surrounding the failure, there could be disciplinary action taken."

Flynn, citing rules on confidentiality, declined to comment on whether his office would open an investigation into the Norton case.

There is enough information on the public record to indicate that the city was aware of at least some of the Nortons' tax problems. According to a certificate of delinquency filed with the D.C. recorder of deeds in January 1989, the city was aware that the Nortons owed more than $25,000 in back taxes and penalties from tax year 1982. Such a notice would ordinarily be filed after there had been some correspondence between the Nortons and the D.C. government, tax lawyers say.

Grant said yesterday that her department's standard procedure is to mail a copy of the delinquency certificate to the taxpayer at the time it is filed with the deeds recorder.

D.C. records also show that the Nortons paid a federal tax lien with a payment of $2,725 in 1984 for federal taxes that were due for various periods from 1979 through 1982. The lien apparently referred to employment taxes -- such as Social Security or income taxes -- that are generally paid by employers for household help.

Baltimore tax lawyer Paula Junghans said it is not uncommon for even the federal government to take up to five years to note a failure to file. "You'd be astonished at how many people do this," she said.

Some tax experts were surprised that once the D.C. government filed the delinquency certificate for 1982, there were no other certificates on file for subsequent years.

"Somebody in D.C. government knew there was a problem with one return, and normally they would look to see if subsequent returns were filed and seek further payment," said one expert, who asked for anonymity.

While it is possible that the statute of limitations would prevent criminal prosecution for offenses more than three years old, there is no limit on the time the District may take to collect the taxes due, experts said.

Staff writer R.H. Melton contributed to this report.