D.C. Budget Director Gladys W. Mack acknowledged yesterday that she does not know fully how well Mayor Marion Barry's cost-cutting program is working -- even though the seven-month period it was designed to cover is nearly half over.

"We are beginning now to get some reliable data" on spending curbs Barry imposed Feb. 28 in an effort to save $50 million this fiscal year, Mack told the Finance and Revenue Committee of the City Council. The program is "pretty much on target." she said, except in the Corrections and Human Services departments -- the two agencies in which overspending was most rampant.

But when asked by committee chairman John A. Wilson (D-Ward 2) for a precise figure on savings to date, Mack replied, "I can't really give you an answer." She said her department is still analyzing information from the city's troubled financial management system.

Barry's program to avert a deficit projected as high as $172 million includes a freeze on hiring and promotions, a ban on overtime pay, and a reduction of the city payroll by 1,540 employes, including 403 by layoffs. An additional reduction of 3,000 jobs has been proposed for the coming fiscal year.

The exchange between Wilson and Mack came at an informal second hearing by the committee into the mayor's proposed tax package, which is designed to raise $20.2 million between July 1 and Sept. 30 to help erase the deficit. The first hearing was held in April.

The mayor has proposed a rise in the general sales tax rate from 5 to 6 percent, a new 6 percent sales tax on the retail price of gasoline; an increase from 1 to 2 percent in the transfer tax on the sale of real estate; a rise in the taxes on business equipment and hotel room occupancy, and a higher tax rate on commercial real estate.

Wilson announced that he has scheduled a committee meeting on Wednesday for a showdown vote on the tax package, which Barry first proposed in early March.

Wilson said he would neither support nor oppose the mayor's proposals in the committee vote, maintaining as he has in the past that they are inadequate to solve both the current cash squeeze and an even larger deficit expected in the coming fiscal year.

He said he wanted to deal with total city problems at one time, and not be forced to consider a second tax rise next fall.

"In my estimation, it's weak leadership," from the mayor," Wilson declared, saying an even larger increase may be necessary to maintain essential city services. Wilson's neutrality left in doubt the outcome of next week's anticipated vote for the five-member committee. Under council procedure, a majority of those voting must support any measure to bring it before the full council for legislative action.

Two other members of the committee. David A. Clarke (D-Ward ) and Polly Shackleton (D-Ward 3) are regarded as supporters of the bulk of the mayor's package, while the other two, Betty Ann Kane (D-Ward 7), are reported as currently opposed, Clarke and Kane confirmed their positions yesterday, while Shackleton and Hardy were unavailable for comment.

During the hearing yesterday the Greater Washington Board of Trade, the city's principal business organization, reiterated its opposition to any tax increase that would burden the business community.The Washington Hotel Association opposed the proposed rise of the nightly hotel occupancy tax rate, from 8 to 10 percent, contending it would make the city less competitive for convention business.

While the committee was meeting Barry made the latest of a series of trips to Capitol Hill to presuade key lawmakers to support higher federal payment to the city.

Yesterday, he met with Sen. Ernest F. Hollings (D-S.C.), chairman of the Budget committee. In earlier meetings, Barry had talked with the chairmen of the two appropriations committees, Sen. Warren G. Magnuson (D-Wash.) and Rep Jamie L. Whitten (D-Miss.), and with Sens. Henry F. Bellmon (R-Okla.) and Birch Bayh (D-Ind.).

The congressional budget committees set the ceiling for the maximum amount that Congress can spend on the federal payment for the District, while the appropriations committees decide on the precise amount to be allocated, within the limit set by the budget committees.