Senate-House conferees hope to finish work this week on a $9 billion supplemental appropriation bill to help some financially strapped U.S. departments and agencies meet their payrolls and other expenses during the remaining three months of this fiscal year.

If agreement is reached, the bill must be approved by the full Senate and House. Then it would go to the president who -- through aides -- has indicated that it needs some work before he will sign it.

Supplemental appropriations are routine -- but important -- and most get loaded up with a variety of catch-all items. In addition to providing money for ordinary operations, this one deals with the scope of proposed drug testing programs in federal agencies and, like previous supplementals, also covers pet programs of members of Congress and the White House.

Although those inclusions and exclusions frequently have little to do with day-to-day operations of agencies they sometimes can result in delays in passage of the bill. The House bill calls for $9.25 billion while the Senate bill, which includes some foreign aid money, is $9.76 billion.

A dozen major departments and many more agencies are asking for funds in the present money bill. Insiders say that as of yesterday, only the Interior Department money package had been tentatively approved. Some agencies need the money more than others and some, according to the employe rumor mill, are talking furloughs or layoffs if they don't get financial relief fast.

The possibility of layoffs or furloughs is frequently raised in these situations. But it isn't always a bluff.

In the past few years some agencies have had short furloughs, and in some cases even more costly and morale-damaging reductions-in- force because of budget crunches. RIFs, especially at the end of a fiscal year, wind up costing the government more than they save over the short haul because fired workers must be given severance pay and be paid for unused annual leave, and their unemployment benefits are charged to their former agencies.

A key house staff aide said yesterday that "there was a meeting on the supplemental situation but the subject of RIFS or furloughs didn't come up."Postal Union Clout

A postal union official says that Monday's column about contract talks between unions and the U.S. Postal Service understated the memberships of both the National Association of Letter Carriers and the American Postal Workers Union. We said the two unions represent about half of the total postal work force. In fact, the two unions -- which have formed a joint committee for bargaining purposes -- have about 570,000 dues-paying members, and represent 600,000 of the service's 800,000 workers -- about 75 percent.

The contract between the U.S. Postal Service and its work force expires late next month.

Job Mart

Agriculture in Hyattsville wants a clerk-typist, Grade 3 or 4. Call 436-7776.

Public Health Service downtown needs a GS 6 administrative aide (typing). Call 443-6900.

Federal Communications Commission is looking for electronics engineers, GS 5/7, and computer programmers, GS 5 through 9. CS status required. Call Clyde Matthews at 632-7106.

Navy in Crystal City is looking for a personnel staffing specialist and personnel classification specialist, GS 9 through 12. Status required. Call 746-0174.