What if Congress failed to enact a budget for the District of Columbia and nobody noticed?

That is just about what has happened this year, as the enactment of the budget for the fiscal year that began Oct. 1 continues to be hung up in a Congressional dispute over the city's proposed downtown convention center.

To keep the city running, Congress has passed two "continuing resolutions" that permit continued spending at the last fiscal year's pace. Because the new budget is largely a hold-the-line budget, with virtually no new programs, its lack is having no noticeable effect on the services that the city provides to its taxpayers.

The main problems caused by the delay are administrative and technical, city officials said.

The current continuing resolution is due to expire Nov. 30, and unless the issue is resolved by then, another resolution probably will be enacted carrying over to next Feb. 28.

Despite home rule, Congress has retained the power to review the city's annual budgets, line by line.

In addition to $1.2 billion in operating funds, the stalled budget would provide about $165 million for new public buildings and such facilities as sewers. The construction money is borrowed from the U.S. Treasury and repaid with interest over 30 years.

Ronald W. Mordecai, deputy director of the D.C. Department of General Services, said none of the public works projects has been delayed, and none is likely to be unless the budget delay is drawn out into next spring.

Ben W. Gilbert, director of municipal planning, said the same situation applies to the convention center, proposed for a site near Mount Vernon Square NW.

If the center is finally approved by Congress within the next few months, Gilbert said the timeable that calls for groundbreaking in 1979 and completion by 1981 can be met.

The pending budget, as voted by the House, contains $27 million in start-up costs for the project, which, it is estimated, will eventually cost $110 million. The Senate ommitted all funds for the project.

The convention center ussue is basically a clash between two lawmakers who led the two chambers to take those opposite positions - veteran Rep. William H. Natcher (D-Ky.), a supporter of the project, and freshman Sen. Patrick J. Leathy (D-Vt.), an opponent of the convention center plan.

As chairmen of the House and Senate District Appropriations subcommittees, Natcher and Leahy faced each other across a table at two sessions of a joint conference committee that tried to agrree on a budget. The conferees deadlocked on the convention center issue, and Natcher has not agreed on a third session. Leahy has said he would meet at any time.

There are other issues between the conferees as well, including the authorized size of the police department (Natcher wants a slightly bigger one than the city proposes) and the amount of the federal payment, which chiefly compensatts the city for its inability to collect taxes on government-owned property.

The House has proposed a federal payment of $295.4 million, while the Senate has proposed $276 million.

Apart from the convention center, the biggest single public works project potentially affected by the budget inaction is $56.7 million for building construction at the Mount Vernon Square campus of the University of the District of Columbia (UDC). The Senate wants that project delayed - briefly, Leahy said - until Congress can review a master plan for UDC construction programs.

Other projects that might be affected by a long delay include a $35 million municipal office building at 4th and D Streets NW: a new Lamont-Riggs branch library in northeast Washington; the modernization of the Bell Career Center (vocational high school), Hiatt Place and Irving Street NW, and the Phelps Career Center, 24th Street and Benning Road NE; development at Fairfax Recreation Center, 41st Street and Alabama Avenue SE, and the Hendley Elementary School playground, 6th and Chesapeake Streets SE, and several sewer, water, and street projects.