The Carter administration yesterday announced three actions that officials said should increase the production of unleaded gasoline required by late-model vehicles equipped with mandatory anti-pollution devices.

The actions, announced at the White House by Energy Secretary James R. Schlesinger Jr. and Environmental Protection Agency Administrator Douglas M. Costle, should shift up to 800,000 barrels a day of gasoline production from leaded to unleaded gasoline, the officials said.

Unleaded gasoline costs more than leaded fuel and generally has been in shorter supply in the overall energy shortage.

The actions announced by the officials will:

Suspend until Oct. 1 a government ban on the use of MMT, a gasoline additive used to increase the octane level of unleaded gasoline.

Relax standards for led in gasoline by allowing an overall average of .8 gram of lead per gallon instead of the .5 gram per gallon standard that was to take effect Oct. 1. The relaxation will be for one year, with the .5 gram standard to be imposed Oct. 1, 1980.

Provide refiners an additional incentive for producing unleaded gasoline by allowing them to charge 2 cents a gallon above the current base price for unleaded gasoline, which is already 1 cent a gallon more than they can charge for leaded gasoline.

Schlesinger said the 2-cent-per-gallon incentive will apply only to production of unleaded gasoline above current levels and should add about two-tenths of a cent to the retail price of unleaded gasoline.

Schlesinger yesterday also defended the administration's decision to provide refiners with a $5 a barrel subsidy for importing heating and diesel fuel.

That decision has been widely criticized in Europe as a move to divert fuel supplies from European countries and was discussed yesterday by French Foreign Minister Jean Francois-Poncet in a meeting with President Carter.

Following the meeting, Francois-Poncet issued a written statement saying he had told the president there is "serious preoccupation" in Europe with what it seen there as a decision "to divert towards the United States a larger share of the oil on the world market."

Schlesinger argued that just the opposite is true. He said the subsidy is an attempt by the United States to halt the loss of some of its traditional sources of supply that have been attracted by Europe by high spot market prices. CAPTION: Picture, Schlesinger explains steps to assure more unleaded gas, at slightly higher price.