Everyone has his favoirte fight with a computer, but the District of Columbia government is taking more than its share of punches learning to cope with its new, allegedly super-duper, computerized financial managment system.

In just four months of operation, the Magnificent system forgot to send Uncle Sam $11 million in December federal withholding taxes for the city's 55,000 workers; left one city contractor fuming while he waited more than a month of get nearly three-quarters-of-a-million dollars in back payments from the city, and is inoperable about half the time.

"It's still a struggle," says Colin F. S. Walters, assistant city administrator for financial management. "The shakedown is going to last for at least the first year."

"Fundamentally, the system's doing quite well," according to Jan Lodal, executive vice president of American Management Systems Inc., the Arlington firm that installed the new system. "But there are lots of operational problems, shakedowns not a lot greater than I expected Oct. 1 (when it started), but a lot greater than I would have hoped for last May or June."

Walters said the paperwork for the $11 million in withholding taxes involved some "computer processing that didn't get done. It got lost in some lesser transactions."

He said he learned Jan. 16 that the payments had not been made to the federal treasury and checks were issued the next day. He said the District is now current in its payments.

But delays in learning how to use the new system, mandated by a federal agency called the Temporary Commission on Financial Oversight of the District of Columbia because of past accounting mistakes in the city, has caused other problems.

Buinessmen with city contracts have often waited for more than a month to get paid while D.C. workers figure out how to get the necessary information into the computer so that the check can be authorized.While in the past D.C. agencies could simply tell the city's financial officers to write a check to pay a bill, now vouchers have to be submitted to show when the services were performed or merchandise received.

"Agencies are simply having to get used to a much more sophisticated system," said one person familiar with the difficulties.

The same person also said that the District government simply did not hire enough new people to adequately run the complex system. Then, when the computer balked at paying city contractors because the proper information was not entered into the machine, checks were written by hand, the old method.

As a result, there now are about 1,500 transactions in which checks have been written by hand that eventually have to be corrected in the computer.

One city contractor, the Tricentennial Energy Corp., waited 35 days to get $727,000 in back payments for oil and finally resorted to making only emergency deliveries in an effort to force the city to pay up.

"If the D.C. government paid its bills on time, we would have a perfect contract," Tricentennial's president, G. H. Starke Jr., wrote the city.

Another person involved in the city's financial operations said that workers dealing with the new system were not adequately trained.

"It's like they took a bunch of oxcart drivers and put them in the cockpit of a 747 and told them, 'Fly it away boys.' That's exactly what's been done here without giving people any training," he said.

"The bottom line is that the thing is screwed up," the source said.

On top of the staffing and training problems, the city's computer has not cooperated much either, according to two people involved in the operation. They estimated that the city's computer is inoperable 40 to 50 percent of the time.

The new financial system grew out of an auditor's complained in 1975 when the city assumed limited home rule powers, that D.C. government books were in such disarray they could not be audited. The temporary commission was established and a new plan devised to cope with the city's $1.5 billion annual budget.

The new financial system has already cost $20 million and Congress has authorized spending a total of $38 million on the project, although the last $13 million of that has yet to be appropriated, according to Robert Stephens, the commission's acting executive director.

A decision was made last summer to start the new management system on Oct. 1, despite some fears that the city government was simply not ready to operate it.

The result is that city officials are now coping with the mistakes in their on-the-job training.