D.C. Council member John A. Wilson (D-Ward 2), charging that Mayor Marion Barry has understated the true cost of his proposed income tax increase, said yesterday that the plan is designed to raise $248.8 million over five years, rather than simply cover a $69 million shortfall over the next two years.

Wilson, chairman of the Finance and Revenue Committee, which met yesterday, said the difference is important because it shows the true, longer-term impact of Barry's proposed repeal of two tax breaks. The mayor, in presenting his $2.8 billion 1989 budget last week, emphasized the two-year effect of his tax proposals, which also included a one-time 5 percent income tax surcharge for 1989.

Barry's finance officials confirmed Wilson's figures. Wilson said that Barry's tax increase plan, if approved, would extend through 1990, the next mayoral election year.

"In 1990 you won't even whisper" tax increase, Wilson said, "That's why you want to do it all in one fell swoop here."

Wilson's remarks came as Barry's taxing and spending policies faced stepped-up opposition in the D.C. Council, with members charging yesterday that the mayor is funding a growing government bureaucracy rather than providing needed social services.

Council Chairman David A. Clarke said in budget hearings that the mayor could avoid a tax increase by eliminating hundreds of new or unfilled staff positions and reducing government overhead costs such as rents and utilities.

In an hour-long grilling of Barry's revenue officials, Wilson and other members of the council disputed the mayor's contention that a projected slowdown of the economy and increasing need for city services are fueling the call for higher taxes.

Wilson said the city's economy is continuing to grow at a healthy rate, though not as rapidly as in previous years. Wilson said the problem is that the government is growing faster than the economy.

Council member Betty Ann Kane (D-At Large) said Barry's aides are projecting that the city will take in an increase of $160 million in revenue from the city's income tax over the next two years even without the higher taxes proposed by the mayor.

"It's unconscionable" to ask for increase with growth that high, Kane said.

Twice last year the council rejected income tax increase proposals by Barry.

Clarke said the mayor could eliminate the tax package by curbing costs.

For example, Clarke said, the mayor has reported $76 million in savings during the current fiscal year by cutting administrative expenses, not service programs. Clarke said if Barry were to do the same thing next year, there would be no need for a tax increase.

Clarke said the increase in employees, together with the growing unfunded pension liability, not only inflates the present budget proposal but also "significantly mortgages the future of the city."

Clarke told the mayor's budget director, Richard C. Siegel, that the city should impose a hiring freeze on nonessential personnel to reduce the expenditures in the proposed budget.

He also asked for a list of employee vacancies, with notes on whether city officials believe the positions are essential.

Siegel, who along with other top city finance officers appeared before the council, said there is no hiring freeze in effect, though agency heads have been told to "hold back" filling some vacant positions.

Clarke also asked if the mayor's proposed budget includes pay raises for some top city officials.

An advisory committee appointed by the mayor last year recommended that salary levels for some Cabinet members be set as high as $95,000 to attract applicants.

Siegel, saying he doubted that the salary levels would be that high since agency heads cannot earn more than the mayor's $83,010 salary, said any increase in pay for department heads would represent "a small portion of the overall budget."

Clarke said he is opposed to pay raises for top city employees.

"Timing is everything," he said. "I don't think this is the time."