J. Q. Citizen: assets - $8,400; liabilities - $4,600

As a shareholder of Uncle Sam Inc., each resident of the United States owns federal assets worth around $8,400. His share of Uncle Sam's debts is a bit more than $4,600.

Looking at the size of the national debt, most people would probably imagine that Uncle Sam is deep in the red. Actually, his assets greatly exceed his liabilities.

That conclusion stems from a new study by three Stanford economists, Michael J. Boskin, Terrance O'Reilly, and Praveen Kumar, and a fourth from the University of California at Los Angeles, Marc S. Robinson. The study, for the National Bureau of Economic Research, looks at two of the most valuable federal assets: mineral rights and land.

In 1982, the four calculate, federal oil rights (onshore and offshore) were worth around $486.8 billion and gas rights about $330.4 billion, for a total of

Those numbers, Mr. Boskin said in a telephone interview, are ''deliberately conservative.'' They are based on US Geological Service (USGS) estimates for 1981 of proven reserves on federal lands, plus the much larger estimates of undiscovered, economically recoverable resources of conventional oil and gas on federal land. In the past, these reserve estimates have typically been revised upward, Mr. Boskin notes.

Then he makes what economists call a ''present value'' estimate of the worth of these rights. Using pessimistic USGS reserve calculations, oil and gas rights could be valued as low as $582.1 billion; with optimistic calculations, as high as $1,134.9 billion. The average reserve estimate results in the $817.2 billion figure. Because the price of oil has slipped since 1981, Mr. Boskin guesses that this average value should be reduced somewhat below $800 billion today.

Looking at federal lands, the paper calculates the value of urban properties (Washington buildings, federal post offices, etc.) at $112 billion and rural land (forests, grazing lands, national parks, military bases, etc.) at $63 billion - a $175 billion total in 1981.

Mr. Boskin admits that such a calculation is based on estimates of per-acre values and is very rough. It would be difficult to put a specific value on Yosemite or Yellowstone National Park, he conceded.

These estimates, however, also ignore the value of other minerals, such as uranium or copper, that are on federal lands.

Nonetheless, his paper points out, ''Ignoring resources in national income and wealth accounts, and government budgeting, can be quite misleading.'' In other words, the sale of oil and gas rights and of federal land can provide important revenues to the government.

Besides these resources, the government owns about $500 billion in buildings, machines and equipment, inventory, military hardware, and other such tangible capital assets. And, Boskin adds, it has another $500 billion of financial assets, such as gold reserves, holdings of government securities by the government, mortgages, and other paper.

Add these up and it comes to almost $2 trillion. That compares with the national debt held by the public of some $1.094 trillion, a figure that excludes some debt held by the Federal Reserve System and by trust funds. Then divide by a US population (around 236 million) and you get per capita figures of assets running $8,400 and liabilities at $4,600.

Of course, as Boskin knows, Uncle Sam could not suddenly sell his assets to get the money to pay off his liabilities. But it is useful for the government to know the value of its assets in its management of its mineral rights and its lands, and for budget purposes. And it may be of some comfort to citizens to know that Uncle Sam isn't destitute.