The nation's unemployment rate edged up slightly in October, the government reported yesterday. It was the seventh month in a row that joblessness has remained essentially on a plateau.

The Labor Department's monthly survey put the jobless rate at 7 per cent of the work force, up from 6.9 per cent in September. Unemployment has hovered between 6.9 per cent and 7.1 per cent since April.

More important, the economy produced far fewer jobs last month than it did in September, indicating the autumn doldrums still have not ended. Total employment rose only by 135,000 jobs, two-fifth of September's increase. And joblessness among blacks rose sharply again.

The various statistics increased the likelihood that the Carter administration will seek a large tax cut next year to stimulate the economy. President Carter has hinted he's leaning that way, but has not made a firm decision.

The administration also is under pressure to end its delay in endorsing the Humphrey-Hawkins "full-employment" bill - job-creation legislation that blacks and some liberals have been urging Carter to support. The White House and congressional sponors have been negotiating on a compromise version, but the talks have been in a lull.

The White House expressed disappointment about yesterday's figures. Rex Granum, the deputy White House press secretary, and the administration was "concerned" that employment did not rise more rapidly.

At the same time, however, Granum told reporters that the administration would "form our fiscal and other economic policies in light of the economic growth we can expect in 1978 and 1979," rather than on the basis of tany single month's statistic. That longer-ranger outlook now seems bleak.

Meanwhile, Republicans took the opportunity to renew their call for a 33 per cent across-the-board cut in income tax rates are as means of stimulating economy. Bill Brock, chairman of the Republican National Committee said Carter's "inaction in this area points up another major broken promise."

The brunt of the added joblessness last month fell on adult men and blacks - raising doubts about officials' assertions in September that a sharp rise in black unemployment last August was only a fluke.

The jobless rate for blacks rose to 13.9 per cent in October - below the 14.5 per cent registered in August, but up from the 13.1 per cent rate in September. The rate for all adult men rose to 4.4 per cent - an eight-month high.

Julius Shiskin, the commissioner of labor statistics, who earlier had dismissed the rise in black unemployment at an aberration, conceded in a telephone interview yesterday he was "not as sure of that as i was last month."

Shiskin said it was becoming clear that while joblessness among whites was receding, unemployment among blacks continues to remain high. "We have two separate economies," he said. "This is a great expansion - for whites."

The figures on job growth were based on a survey of 47,000 households. Another measure, tabulating industry payrolls, showed job levels rising by 120,000. However, that figure was depressed by a strike in the aircraft industry.

Along with the other figures, the Labor Department reported a slight rise in the length of the average workweek - ending the slide that has continued for the past few months. The workweek rose a scant 0.1 hours.

At the same time, the average hourly earnings of rank-and-file production workers rose a hefty 1.3 per cent - possibly foreshadowing sizable increases in personal income just before the Christmas shopping season.

The sluggishness in new job growth came in the [WORD ILLEGIBLE] of a moderate increase in the number of new job-seekers. The size of the civilian labor force rose by 234,000 in October, up from a 171,000 rise in September.

Yesterday's report brought the number of persons out of work to 6.9 million - up 99.000 from September's level.

The latest rise in employment was among the smallest in recent months. The number of new job grew by 324,000 in September and 210,000 in August.