The unemployment rate remained virtually unchanged last month, even though the Labor Department reported a big increase in the number of Americans with jobs.

The department said joblessness fell slightly from 7 per cent to 6.9 per cent of the work force. It was the eighth month in a row that the rate has been stuck between 6.9 and 7.1 per cent, and White House press secretary Jody Powell acknowledged that the administration has little chance to reach its goal of driving unemployment down to 6.5 per cent by the end of the year. 'It's not likely to be there," he told reporters.

According to the less reliable of the two employment surveys the department makes each month, the number of persons with jobs rose a phenomenal 950,000 in November, but this had only a marginal impact on the unemployment rate because the number looking for jobs also rose sharply, by 900.000.

According to the other, more dependable job survey - which is based on actual payrolls rather than a sampling of households - the number of people with jobs rose 310,000. Even that is a large increase by normal standards, and a sign the economy could be turning up from its summer doldrums.

Julius Shiskin, commissioner of labor statistics, told Congress' Joint Economic Committee he could not account for the unusual discrepancy between the two surveys. He said the 950.000 number from the household survey was probably inflated. Other federal analysts suggested that part of the problem may have been a faulty system of adjustment for normal seasonal job fluctuations.

The Labor Department has been having troubles with its montly employment and unemployment figures in recent years. Its analysts have found it difficult to cope, on a month-to-month basis, with changes in the composition of the labor force (more women are working) and with distrotions in the normal seasonal patterns of employment and unemployment that were caused by the recession of 1974 and 1975.

Even if the November employment increase was exaggerated in the household survey, Shiskin told the joint committee that "the increase over the past 12 months - 3.9 million - has been very impressive."

But he noted that the big increase in employment over the year was accompanied by an "unusually large" increase in the number seeking work. About 3.2 million persons joined the labor force: annual increases in recent years have averaged about 2 million.

In the current year the unemployment rate has fallen from 8 per cent to 6.9 per cent, with most of the improvement coming in the early months. President Carter hopes his proposed large tax cut next year will reduce the percentage further.

Women continue to account for most of the increase in the labor force, which is the total of those who have jobs and those who are actively looking for them. Of the 3.2 million year-to-year increase in the work force, 1.7 million were adult women, 1 million were adult men and 500,000 were teenagers.

Last month, about 450,000 women, 280,000 men and 125,000 teenagers found jobs. The unemployment rate - the percentage of the labor force seeking work - declined to 4.9 per cent from 5.3 per cent for adult men, rose from 6.8 per cent to 7.1 per cent for women, and fell to 17.1 per cent from 17.3 per cent for teenagers.

The black unemployment rate was 13.3 per cent compared with 13.9 per cent in October.

Over the year, while the white unemployment rate has declined from 7.3 per cent to 6 per cent, the black unemployment rate has risen slightly from 13.5 per cent in November, 1976, to 13.8 per cent last month.

The total labor force was 99 million in November, compared with 95.3 million a year ago. The number of persons at work rose to 92.2 million from 88.3 million a year before. There were 6.8 million Americans looking for work last month, nearly the same as in October but 800,000 fewer than a year ago.