Any money Congress adds to the defense budget this year will not go for new weapons.

Instead, the Carter administration has notified the Senate, additional money would be spent on such unglamorous items as maintaining existing equipment and paying the higher gasoline and electricity bills of the U.S. military establishment.

Several key senators are demanding increased defense spending as their price for supporting the pending strategic arms limitation treaty.

Sen. Sam Nunn (D-Ga.) for example, has written President Carter that defense spending should be increased by 4 to 5 percent a year to make SALT II an acceptable risk for the nation.

Critics have attacked Nunn's linkage of higher defense spending with SALT II on two grounds: the extra billions would not be used for strategic weapons of the kind covered by the treaty and the Pentagon could not wisely spend that much additional money in any other way, either.

The Joint Chiefs of Staff, while acknowledging there is no quick way to close the blockbuster missile gap with the Soviets, have insisted they could use extra billions to maintain the arsenal and forces in being.

It is this case the Pentagon makes in its newest shopping list to be cited in the Senate debate today. Here is how the Pentagon would use extra billions in fiscal year 1980:

Fuel, $888.5 million Cater, the Pentagon said, figured oil would cost $19.30 a barrel rather than the actual price of $24.50. With ships, tanks and planes burning about 170 million barrels of fueld in fiscal 1980, almost $1 billion more is needed.

Dollar plunge, $470 million. "The anticipated improvement" in foreign exchange rates for the U.S. dollar "has not taken place, nor does it appear likely to occur at any time in the near future." More money is needed to cover wages and other activities paid in foreign currency.

Utilities $113.3 million. This covers higher-than-expected heat and light bills at military installations.

Higher moving expenses for household goods. $175 million.

Stepped-up recruiting of volunteers for the armed services, $51.9 million

Supplies and services, including janitors and kitchen help. $556.6 million.

Other items on the list, such as higher allowances for service people living overseas, industrial purchases and repair depots for aircraft, push the total up to $2.7 billion. This is the amount President Carter planned to add to the Pentagon budget he sent to Congress in January.

However, Hollings and his allies estimate it will take a bigger hike to achieve a 3 percent "real" growth in the fiscal 1980 defense budget because of spiraling inflation.

Also, the Hollings forces will seek to increase defense spending by 5 percent in fiscal 1981 and 1982.

The starting point for these increases is previously imposed congressional ceilings for national defense of $136.8 billion in budget authority and $127.4 in spending for fiscal 1980.

Hollings will propose new ceilings for fiscal 1980 of $141.2 billion in budget authority and $130.6 in spending, increases of $4.4 billion and $3.2 billion, respectively.

The higher ceilings for fiscal 1981, under the Hollings amendment, would be $159.8 billion in budget authority and $145.6 billion in spending. For fiscal 1982, the totals would jump to $180.4 billion and $163.3 billion in budget authority and spending.

Although the fiscal 1980 additions would not buy new weapons, Hollings and his allies intend to argue that the less glamorous accounts are just as vital for the national defense. Some of the proposed increases for fiscal 1981 and 1982 could go for new weapons, according to Hollings.

Opponents of higher defense spending intend to argue today that preestablished hikes invite Pentagon waste, strategic weapons already have all the money that can be wisely spent and that the Hollings amendment would fuel inflation and undercut efforts to reduce the federal deficit.