The D.C. City Council agreed informally yesterday to discontinue leasing a car for its chairman and to eliminate other perks for council members in an effort to cut rising operating costs and avoid potential budget deficits.

The savings for the current year, which already is three months old, were not certain. In the 1984 fiscal year, however, which begins next Oct. 1, the cuts would trim about $313,000 from the council's spending request, including $2,100 for the leased car and $234,534 in personnel costs.

The action by the 13-member council, if formally ratified at a regular meeting next month, would mean that about 10 of the council's authorized 139 staff positions would remain vacant this year and next.

The members, led by Council Chairman-elect David A. Clarke, agreed to give up about $81,000 in office supplies and expenses--including car telephones that would cost a total of $16,000, photocopier expenses totaling $20,000 and electronic pagers that would cost a total of $3,300 per year.

In addition, the council members, who spent a total of $57,000 on postage last year, agreed to limit each member, including Clarke, to $2,000 a year.

The cuts would reduce the council's proposed budget for fiscal year 1984 to $5.4 million -- still an increase of about $417,000 over the current fiscal year that began Oct. 1 this year.

The council decision to trim its own budget comes just a few weeks before it begins oversight hearings on the proposed 1984 budget for the entire city, which may top $2 billion. It is to be released by Mayor Marion Barry Jan. 10.

Barry also is expected to propose revisions in the current fiscal year budget to make up for a potential deficit of $110 million because of declining revenues and rising costs.

Council staff members said the council over the past few years has routinely used unfilled staff positions to pay its operating costs, but that the amount has steadily risen from about $300,000 a year to the nearly $500,000 this year.

Clarke said council members also plan to hire top assistants at lower pay grade levels, including his own executive assistant, who may be paid about $8,000 less than authorized.