Agency heads, budget officers and attorneys are trying a variety of approaches, from little-used financial transfer authorities to prayer, to avoid or minimize the impact of furloughs that could hit as many as 70,000 government employes from astronauts to tax-collectors.

More than a dozen agencies had September salary money riding on the supplemental appropriations bill that President Reagan vetoed Saturday.

Because of the veto, many government departments, or portions of agencies, are about to run out of money. Many have already alerted employes that they may have to be furloughed for part or most of September, the last month of this current fiscal year.

Here's what some major agencies face unless Congress (which is not due back until Tuesday) and Reagan work out their differences:

The Internal Revenue Service has asked congressional appropriations committees to let it transfer money from one account to another to avoid beginning furloughs as early as Friday for several hundred Washington-based workers involved in collections and crime enforcement.

If IRS gets a reprieve this week, it still faces the prospect of having to furlough as many as 20,000 people -- nearly half its staff -- later this month.

The U.S. Secret Service is also in a salary bind. Although it can obligate funds to keep paying agents assigned to guarding the president, it may have to furlough support personnel.

National Aeronautics and Space Administration has alerted 22,000 workers, including 5,000 here at headquarters and at Goddard Space Flight Center, it may have to furlough them for up to 10 days this month. NASA has a daily payroll of about $3 million and it had a $31 million payroll request in the vetoed supplemental.

NASA officials believe that by cutting other costs (travel and purchases) they may be able to limit the furlough to only a few days this month.

Other agencies in varying degrees of financial distress include big chunks of the Justice Department, Office of Management and Budget, Office of Personnel Management, Federal Labor Relations Authority and portions of the White House itself.

The Smithsonian Institution, which had been on the potential furlough list, says it can avoid furloughs and shutdowns by tranferring money from other accounts, although it, too, had money requests in the supplemental.

The furlough situation can, and will, change from day-to-day. Even if furloughs are ordered they can be canceled at the very last minute -- if Congress and the White House finally come up with money.