Wholesale prices shot up last month at their fastest pace since last spring, the government said yesterday.

The Labor Department's index rose a staggering 0.8 per cent in October, the agency announced, substantially more than the 0.5 per cent of the previous month, and the largest increase since April.

Most of the increase was in farm and food prices. Raw agricultural prices leaped 2.4 per cent, following five months of sharp declines. Prices of processed foods and feeds rose 0.8 per cent, after dipping 0.6 per cent the month before.

Industrial prices, considered a more reliable bellwether of future inflation trends, rose 0.6 per cent in October, easing back somewhat after an 0.8 per cent spurt in September that ended four months of moderation.

Although the October figures were disappointing, analysts were cautious about interpreting them. Maynard S. Comiez, the Commerce Department's deputy chief economist, warned that many of the price increases were apt to be of the one-time only variety.

Comiez said it was unlikely the increases in farm prices would show up quickly at the retail level because supermarkets had been able to widen their profit margins recently and probably would absorb them.

The White House was sanguine about the increases. Jody Powell, the President's press secretary, said while officials were "disappointed . . . we do not believe this represents any acceleration" in the basic inflation rate.

The October rise brought the pace of inflation at the wholesale level over the past three months to an annual rate of 5.5 per cent - up sharply from the 1.9 per cent recorded for the period ending in September.

The department's index of finished goods prices, which most closely parallels the makeup of the consumer price index, rose 0.8 per cent in October - double its September pace.

The increase in farm and food prices was concentrated primarily in prices of livestock, meats, grains, poultry and vegetables. The index showed declines in prices of eggs, sugar, coffee, cocoa beans and milk.

On the industrial side, the largest boosts were for transportation equipment - reflecting a one-time jump in truck prices at the start of the model year. Jewelry prices also went up more sharply than usual.

Lumber prices continued to rise, but at a pace far below the 4 per cent a month that had prevailed for most of the summer. The increase for lumber and wood prices was 0.8 per cent.

Separately, the department reported that about 11.8 per cent of the average $424.49 price boost in 1978 model cars represents improvement in quality, rather than simple cost pass-ons.

The quality changes were estimated to account for $40.80 of the increase at the wholesale level and $50.12 at retail. The retail figures included $9.99 for redesign of emission controls and $40.13 for other changes.

The October increases brought the overall wholesale price index to 196.3 per cent of its 1967 average. That means it took $196.30 to buy the same goods at wholesale last month that sold for $100 a decade ago. Wholesale prices have now risen 5.9 per cent in the last 12 months.