Sam Nakagama is a well-read economist. In writing his weekly newsletter, he often quotes historians, speeches by world leaders, the latest books, classic literature, even poets.
In his latest ''Economic Perspectives,'' Mr. Nakagama cites T. S. Eliot, who termed April ''the cruelest month.'' That's because he expects answers this month to four hard economic questions:
* Will oil prices plunge further because of the current oversupply, or will the OPEC nations successfully defend the $29 figure?
* Will housing starts maintain the 1.7 million level reached in January-February and will auto sales show the traditional spring pickup after a disappointing winter, thereby keeping the recovery going well?
* Will the growth of the nation's money supply (M-1) slow enough to permit the Federal Reserve System to avoid a major tightening of credit?
* Will the White House and the Senate Republicans be able to agree on a budget plan that will lead to a deficit-reducing compromise with the House Democrats?
Says the economic consultant: ''What happens in April will greatly influence how the economy will behave for the next year or two.''
After being chief economist at Kidder, Peabody & Co. for about 11 years, Mr. Nakagama launched his own consulting firm in February, Nakagama & Wallace Inc. The Japanese-American consultant has a sufficiently good forecasting reputation that enough corporations, including some of the giants, have signed up at around some of his ideas, based on a telephone interview and his latest letters:
Mr. Nakagama believes it likely that oil prices will fall further, despite the apparent decision by the British National Oil Corporation and Nigeria to hold to the OPEC price line for the time being.
Unlike many other economists, he believes a petroleum price war would benefit the world economy only if nominal interest rates declined. ''When the world economy is viewed as a closed system,'' he reasons, ''the gains of oil consumers must exactly equal the losses of the oil producers. Thus, there is no net gain for the world economy in the short run. Indeed, the cutbacks in oil production and investment will occur immediately, while the increases in spending based on savings from lower oil prices will occur with a time lag. If the oil producers - including Saudi Arabia - tried to maintain their previous level of spending, they would be able to do so only by borrowing or selling financial assets, i.e., by dissaving.
''In order to maintain overall spending in the world economy, therefore, the increased dissaving of the oil producers would have to match the increased savings of oil consumers. In other words, the oil producers would have to borrow back the oil savings of the consumers or sell them financial assets. To the extent that the oil producers become poor credit risks - as in the case of Mexico, Venezuela, and Nigeria - they will have little choice but to cut their spending. Since the imports of the oil-producing countries must decline, the exports of their trading partners - industrial and non-industrial - must suffer.''
So the United States economy would be hit in the short run by reduced exports to the oil-producing countries and by a weaker domestic oil industry. The number of drilling rigs in operation has already fallen 26 percent since late December. It could also have ''shock effects'' on the international banking system, since such oil producers as Mexico would have further trouble servicing their debts.
To deal with this problem, Mr. Nakagama urges that Congress pass an oil import tax. He would rebate the tax to Canada, Mexico, and Venezuela, even if contrary to world trading rules.
Federal gasoline sales taxes did go up last Friday. But a further tax on oil imports, Mr. Nakagama figures, would have the benefits of being basically a tax on the OPEC producers, of giving the domestic oil producers a competitive advantage, and of improving federal revenues by perhaps $30 billion. That extra money, he figures, would make it easer for the Senate and the House of Representatives to reach agreement on a budget that would increase somewhat both defense and nondefense spending, but still manage a declining deficit.
Mr. Nakagama also wants the Federal Reserve to exercise more monetary restraint. The measure of the money supply known as M-1, which includes cash and accounts that can be used freely for check-writing, has been growing at a rapid 14.1 percent annual rate over the last six months. Despite the concern that tighter money and higher interest rates might harm a ''fragile'' recovery, Mr. Nakagama insists that ''. . . the Fed runs a real danger of losing control of monetary policy if it pays too much attention to political demands for lower interest rates.'' That would eventually mean another burst of sharp inflation.
Mr. Nakagama suggests that the Fed should bring M-1 growth within its target of a 4 to 8 percent increase in 1983.
He also notes that another measure of money that includes M-1 plus some savings deposits, known as M-2, has been growing rapidly, too. This is primarily the result of the introduction of money market deposit accounts, which have grown in a few months to $318 billion.
''Since this is likely to be a relatively stable source of funds, the banks and thrift institutions can be expected to begin lending more aggressively before too many weeks have passed,'' he says. This could especially help the mortgage market and housing industry, and thus ''the Fed can afford to be more restrictive.''
Mr. Nakagama regards the restrictive policy of the Fed for the last three years as ''a tremendous victory for civilization.'' It meant slow enough growth to cause the ''collapse of OPEC'' and to reduce dramatically the inflation rate in the US.
The latest economic news shows an economy recovering by fits and starts. The government's ''flash report'' for gross national product - the output of goods and services - shows growth in the first quarter running at a 4 percent annual rate. Unemployment declined in March to a 10.3 percent rate.
Mr. Nakagama sees in the situation ''a threat and an opportunity.'' He hopes Congress and the Fed will choose the opportunity.