Sometimes even Uncle Sam, the biggest spender of them all, gets a notice of "insufficient funds."

Federal agencies are preparing for the unthinkable - not enough cash to meet the payroll - in a variety of ways. They range from juggling paycheck deductions to arranging for low-cost bank loans to tide some workers over next week, which will be rough.

At issue is the lack of funds to pay full salaries to more than 43,000 Labor Department and HEW workers here. Also due for half pay are nearly 200,000 of their colleagues outside Washington.

The problem is that there is not a fiscal 1978 appropriation for Labor and HEW. The $60 billion package is deadlocked because the Senate and House cannot agree on the issue of federal funding for abortions. By law, agencies cannot spend after the first of the fiscal year - Oct. 1 - unless Congress says they can. Paychecks of members of Congress, by the way are not affected.

This is not the first time that government departments technically have run out of money to spend. But the normal drill is for Congress to vote a "continuing resolution," which lets paychecks and other things flow pending a return to normality."

Congressional leaders say there will not be a "continuing resolution" this time, apparently planning to hang tough - with somebody else's money. That is why there is unhappiness among HEW and Labor workers who, along with their families, have grown accustomed to eating regularly. So, this is what is happening:

Community Services Administration has arranged for low-cost, short-term loans for its 375 employees here to cover the Oct. 17 paychecks, which will be short. The National Bank of Washington has agreed to cut red tape and offer favorable (8 per cent) loans to CSA people who agree to pay it back next month. Officials say the interest will be only a few dollars for each employee, and the total loans could amount to $120,000 if everybody in CSA takes advantage of the offer.

Graciela Olivarez, director of the antipoverty agency, said the extraordinary loan arrangement was worked out over the Columbus Day long weekend. She pushed it, she said yesterday, because "I can't see myself heading a poverty-fighting agency and contributing to a problem "that would put many of her employees at least temporarily in the poverty ranks.

HEW Secretary Joseph Califano is using a carrot-and-stick approach on Senate and House leaders to get the money bill rolling. Califano pointed out to Senate Majority Leader Robert Byrd that the delay could cut off black-lung payments to 475,000 recipients next month.

Many of those people live in Byrd's home state of West Virginia. Califano also highlighted the impact in states whose representatives on the Hill, coincidentally, stand tall on the appropriations committees.

Because of fiscal year split the next HEW paycheck right down the middle, most workers will get only half pay next Tuesday (Oct. 18). To make that go a little farther, HEW has arranged to pump the maximum amount of money into that half check by temporarily eliminating deductions for savings bonds, charitable contributions and the like. Taxes and retirement deductions will be taken from the checks, which will represent one week's work. Other deductions will be deferred.

Labor Department workers who are due to get paid next Monday also will get checks representing only half the pay period (one week). Labor is taking steps to waive temporarily deductions from those checks, and is geared to make retroactive payments when Congress clears the appropriation and President Carter signs it.