The Carter administration raised the possibility yesterday that it may propose an increase in some gasoline taxes to discourage motorists from tearing out anti-pollution devices in the face of the unleaded gasoline shortage.

The disclosure was made by presidential anti-inflation adviser Alfred E. Kahn during testimony before a House Commerce subcommittee. The proposal would raise taxes on leaded gasoline and reduce them on unleaded gasoline.

Other administration officials cautioned later that Kahn merely was citing the plan as an option, and did not intend to imply that it was under active consideration or was likely to be proposed soon.

However, planners said the Environmental Protection Agency has advocated removing the disparity between prices of leaded and unleaded gasoline to reduce the incentive for car owners to flout EPA rules on anti-pollution gear.

Under present regulations, late model cars must be equipped with catalytic converter anti-pollution devices, which require unleaded gasline.Carmakers say using leaded gasoline will burn the converters out.

However, with unleaded gasoline at least a nickel a gallon more expensive than leaded regular, authorities say many motorists simply have switched to leaded fuel. The recent shortage of premium unleaded gasoline has exacerbated this trend.

Kahn's statement came as top administration economic officials met privately to review 1979 policy recomendations-including one early morning session at the White House.

Meanwhile, Douglas Fraser, president of the United Auto Workers, said his union was seriously considering demanding short-term contracts next year as a hedge against inflation.

Fraser said union officials felt "it might not serve the best interests of our members in this unsettled economic climate to bargain for a three year contracts." He said the union may seek the right to reopen talks after a year.

The move, which could set a precedent for other big union negotiations next year, would be in line with Carter's new wage-price guidelines. Officials have urged unions that felt they needed more protection to settle for shorter terms.

Separately, the Commerce Department reported that new orders for durable goods-considered a key indicator of the economy-declined a sharp 0.9 percent last month after three months of sharp advances.

The statistic was one of the few adverse economic reports to come in the past few weeks. Although many economists still are predicting a mild recession in 1979, the indicators the past few weeks have been relatively robust.

In his testimony, Kahn also told the Commerce subcommittee the White House still has not decided whether to seek an end to controls on gasoline prices. But he forecast that eliminating controls now could boost gasoline prices 7 to 10 cents a gallon.

Kahn's disclosure on the proposal to shift the levels of gaoline taxes came in response to a question from the subcommittee. Asked about the plan, the anti-inflation chief replied: "That's . . . a possibility that we are examining."

However, other officials suggested the presidential adviser may have inadvertently exaggerated the seriousness with which the plan currently is being considered.

"As far as we know," said one, "It hasn't gotten off the back burner."