Some readers, and some federal officials, have called with questions or complaints about Wednesday's front page story about the giant federal vehicle fleet. They want more details or clarifications.

Several callers said they didn't believe the government has, as reported, 450,000 civilian vehicles. That would work out to one for every six employes. Nor could they understand the data that Uncle Sam spends more than $700 million a year -- using 338 million gallons of gas -- maintaining the four-wheel fleet.

Some federal officials, who had no basic quarrel with the story, wanted to know who "talked." They will have to do their own reporting.

For the record, here are the hard facts. They come from the official vehicle fleet report (September 1977) of the General Services Administration. It shows:

The government had 88,394 sedans, 12,237 station wagons, 3,587 ambulances, 10,648 buses and 313,401 trucks. That comes out to 432,267. In addition, GSA had records of another 7,600 leased vehicles. In addition to that, many agencies lease on their own.

Total operating cost for the fiscal year for vehicles was $676,395,384. Mileage was 3.3 million. The official overall average cost per mile was just over 20 cents. The total gallons of fuel used was 338,480,514.

GSA confirms that the gasoline used is "the equivalent to the gasoline content of 17,447,449 barrels of crude oil."

The GSA report also confirms that most of the sedans in the government fleet are "compact class two" or "midsize class three" types. The first group includes such cars as Skylarks, Cadillac Sevilles, Novas and Aspens.

The second group includes cars in the class of the Matador, Malibu, Cutlass and LeMans. They are considered "midsize" by the government.

Only one car in the government classification is considered a limousine. That is the Cadillac limousine.

The State Department was listed as having one limousine in inventory, and the Treasury Department had six. Treasury officials say the six are not used by them, however, but are special models built for the Secret Service for transporting the president and visiting VIPs.

Of the $61 million in vehicle rental costs listed by the GSA, Army ($9.9 million), Navy ($8.1 million) and the Department of Transportation ($5.5 million) led the list.

The report also shows that the number of government cars has been increasing steadily. So have miles driven and -- for obvious reasons -- prices of upkeep and fuel.

Plain Brown Wrapper Department: Help wanted ads in local newspapers have asked for a speechwriter and a feature writer ($22,500 to $31,500) to apply. The address given was a newspaper box number, listed to a government agency. That agency is the U.S. Postal Service. Some of its staffers are unhappy that it went undercover, and outside, in its talent hunt.

Interior has been given approval to fill the top public affairs job in its Heritage Conservation and Recreation Service with a noncareer worker. That means the person selected for the GS-15 $38,160 job will not have regular civil service job protections, or be able to qualify for tenure.