A report on poverty in the U.S., released this week by the U.S. Census Bureau, is sure to provide ammunition for the presidential campaign. But voters may be confused as both parties use the same Census data as proof for opposing arguments.

The Reagan administration and George Bush will point to the good news, and there is plenty. For example, the study shows:- Median family income grew 1 percent in 1987 to $30,850. It was the fifth consecutive year there has been an increase.

- Per capita income grew 1.6 percent to $12,290, an all-time high when adjusted for inflation.

- Median income for families headed by single mothers was reported at $14,620, a significant 3.4 percent increase.

- The number of people below the poverty line remained at 13.5 percent, essentially unchanged from the previous year, while it declined by 7 percent for people living on farms. The study used the federal definition of poverty, namely $11,611 for a family of four. There is no adjustment for regional differences, say between rural Utah and Manhattan.

- The poverty rate for people over 65 stands at 12.2 percent and has been cut in half since 1970.

Yet Michael Dukakis is sure to seize on the negatives of the same report to bolster his campaign. For example:

- While the median income of white families was up, it did not substantially change last year for blacks or Hispanics.

- The poverty rate for whites dropped to 10.5 percent, but it grew 2 percent for blacks to 33.1 percent and stayed at 28.2 percent for Hispanics.

- Forty percent of those living under the poverty level were children under age 18.

- The richest 20 percent of the population earned 43.7 percent of all family income last year, compared to 40.4 percent 20 years ago, and 42.7 percent five years ago. The poorest one-fifth of the population earned 4.6 of all family income, down from 4.7 five years ago.

Politicians will probably use the Census report this fall like some people use the Bible, citing their favorite references to prove a point - and ignoring the rest.