The nation's unemployment rate fell last month, the government reported yesterday, but the economy created few new jobs, and analysts said the overall job picture was little changed.

The Labor Department said the jobless rate dropped to 5.9 percent in August - essentially holding its own after bouncing from 5.7 percent in June to 6.2 percent in July.

But the dip came primarily because the number of persons entering the job market increased less than normal in August.

The total number of jobs in the economy - the statistic analysts use as a key measure of economic growth - rose by only 156,000, a little more than half what is regarded as a good performance.

And industry payroll jobs increased by only 113,000.

The figures mean the jobless rate is stuck on the 6 per cent plateau that has prevailed most of this year. Employment has risen sharply, but so has the number of people seeking jobs.

Most analysts expect the economy to produce fewer jobs in the months ahead, pointing to the likelihood that the jobless rate will not improve dramatically during 1979.

Some economists say the unemployment rate may rise slightly in the next few months.

Nevertheless the August decline served to confirm officials' views earlier that the increase posted in July did not represent a long-term worsening of the job picture.

Jody Powell President Carter press secretary, said the administration was "encouraged" by the August figures, noting that the rate has fluctuated erratically for several months.

The bulk of the improvement in August stemmed from a decline in unemployment among black women and black teen-agers. Joblessness among other major groups of workers remained unchanged.

The jobless rate among blacks fell to 11.7 percent - its lowest level since last April - down from 12.5 percent in July. The rate for white workers held steady at 5.2 percent.

At the same time, the politically sensitive unemployment rate for teenagers fell to 15.6 percent over the month, down from 16.3 percent in July. Here, too, the bulk of the improvement was among blacks.

What was disappointing to most analysts was that the number of new jobs in the economy was so small last month, marking the second month in a row that overall job growth was weak or declined.

In the figures on total employment, the bulk of the increase came from government summer teen-age job programs, which are scheduled to end in September. Analysts say the jobless rate could rise then.

Along with the slower growth in job levels, the department also reported another possible sign of a more sluggish economy, the length of the averate work week continued to shrink, this time by 0.1 hour.

Because of the decline in the work week, the average weekly earnings of production workers also edged down marginally, even though average hourly earnings rose 0.2 per cent.

Yesterday's figures brought the number of people out of work to 5.9 million, down from 6.4 million in July. The overall size of the labor force - jobholders and jobseekers combined - rose a modest 94,000.

The rapid growth in the number of jobs in the economy earlier this year already has enabled the administration to achieve its goal of pushing the unemployment rate to 6 percent or less by the end of 1978.

However, because the economy is slowing from its earlier pace, most analysts are skeptical that the White House will be able to get the jobless rate much lower in the foreseeable future.

The umemployment rate was 7.4 percent when President Carter took office in January 1977.