The government yesterday raised the income benchmark it uses to determine whether a person officially is living in poverty-boosting it to $6,700 for an urban family of four, up from $6,200 last year.

The $500 increase was intended to offset the impact of inflation, which reduced the purchasing power of poor families. The poverty level for a rural family of four was raised to $5,700 up from $5,270 in 1978.

The figures are used in compiling the government's definition of "economically disadvantaged" persons in determining who can qualify for special benefits to the poor and job-training and counseling programs.

The calculation is made each April for the continental United States and, separately, for Alaska and Hawaii. The poverty level for an urban family of four in Alaska now is $8,380. In Hawaii, it is $7,710.

The continental-U.S. figures include this breakdown for urban workers:(TABLE) Family size(COLUMN)1979(COLUMN)1978 1(COLUMN)$3,400(COLUMN)$3,140 2(COLUMN) 4,500(COLUMN) 4,160 3(COLUMN) 5,600(COLUMN) 5,180 4(COLUMN) 6,700(COLUMN) 6,200 5(COLUMN) 7,800(COLUMN) 7,220 6(COLUMN) 8,900(COLUMN) 8,240(END TABLE)

The consumer price index last year rose 9 percent.