The nation's industrial output slowed almost to a halt last month, the government reported yesterday, but analysts said the slackening was only a breather after months of robust increases, and did not portend a slowdown.

Figures compiled by the Federal Reserve Board showed industrial production up a scant 0.1 percent in January, following a jump of 0.7 percent in December and similar increases in each of the several previous months.

At the same time, the Commerce Department announced that business inventories rose 0.6 percent, or $2.37 billion in December, following a sharp 1.1 percent, $4.1 billion rise the previous month.

The falloff in industrial output was not viewed as alarming. At least part of the shift stemmed from bad weather shutdowns and a dip in auto production. Production in previous months had been spurred by a backlog of orders.

Meanwhile, economists for The Business Council, an organization of top industrialists, altered their earlier forecast for 1979 to predict a mild recession rather than simply a period of slower growth.

The Business Council forecast essentially is a poll of corporate economists, and is viewed as valuable primarily as a reflection of business sentiment. The group predicted there would be little progress against inflation.

The slowdown in industrial production was spread throughout virtually every sector of the economy. However, it was especially visible in production of durable goods and business equipment, which remained basically stable.

The decline in auto production was the second in a row. Auto assemblies fell 4 percent to an annual rate of 8.9 million units, from 9.3 million in December. Truck production also fell off.

Analysts said at least part of the fall-off stemmed from bad weather in the north and central industrial regions, which forced plant shutdowns in some areas, particularly affecting steel output.

However, economists cautioned against interpreting the report too pessimistically. Although most analysts expect growth to slow some from last quarter's pace, few economists see signs that the recession actually has begun.

Despite the dip in output of durable goods, production of construction supplies rose a respectable 0.6 percent and output of nondurables climbed 0.3 percent. Production of materials remained unchanged.

Overall, industrial production levels were 8.6 percent higher last month than at this time a year ago. The index stood at 150.7 percent of its 1967 average. The January 1978 report also was affected by adverse weather.

The shift by the Business Council's economists brought the forecast of that group essentially into line with that of most other private economists.

Clifton C. Garvin Jr., chairman of Exxon Corporation, who made public the Business Council report, said almost half the corporate economists surveyed feared the slump would prompt policymakers to impose mandatory wage-price controls.