The Reagan administration's proposed personal income tax cuts would reduce the marginal tax rate for a median income family of four by only a single percentage point between last year and 1984, according to a Treasury Department analysis released yesterday.

Such a family, which for purposes of the analysis Treasury estimated had a $25,400 income last year, paid a 24 percent marginal rate for 1980 and still would pay a 23 percent rate in 1984. These results are similar to those of a Washington Post study of such rates published earlier this week.

It was the first time the administration has provided estimates of changes in marginal rates for 1981 and later years that incorporate the impact of inflation. As incomes rise along with prices, taxpayers can be pushed into higher and higher marginal tax brackets even though their real incomes may not have risen at all.

Administration economists argue that rising marginal tax rates are a source of much of the nation's economic difficulty and that those rates must be reduced to give all taxpayers large new incentives for work, saving and investment.

The reduction in rates under the administration's three-year proposal, would be much larger for a four-person family with twice as much income, or $50,800, in 1980. That family's marginal rate would be lowered from 43 percent last year to 36 percent in 1984. However, the same family with the same real income paid a 37 percent marginal rate as recently as 1979, according to the analysis.

The administration, however, stresses that, if there were no tax cuts between now and 1984, the marginal rate for the median-income family would rise to 32 percent from last year's 24 percent. The higher-income family's rate would climb to 49 percent from 43 percent. These and other estimates assume prices will increase 35 percent between 1980 and 1984, the administration's official inflation forecast.

For a family of four whose income last year was one-half the median, or $12,700, the marginal rate would drop from 18 percent in 1980 to 15 percent in 1984. The rate for such a family in 1979 was 16 percent. Without a cut, the rate would rise to 21 percent in 1984.

Critics of the administration's multiyear tax cut and its emphasis on rising marginal rates say that if rising rates are a major source of economic problems, the administration's plan probably will not solve those problems because marginal rates for most taxpayers will not be much lower in 1984 than they were in 1979 or 1980. However, even among such critics, there is a broad consensus that taxes should be reduced significantly.

For tax purposes, an individual's taxable income is divided into chuncks. On the first chunk, no tax is due. On the next chunk, a 14 percent rate is charged. On the next, 16 percent, and so on as the taxpayerhs income rises. The marginal rate is the rate charged on income that falls within the last chunk, or bracket.

For a four-person family to have a median income means that exactly one-half of all such families have incomes that are higher.