The doubled quota for Indochinese refugees coming up to the United States, announced by President Carter yesterday, is not likely to take effect until October at the earliest, according to State Department and congressional sources.

"You can't go from 7,000 [Indochinese refugees a month] to 14,000 overnight," said one State Department official concerned with refugee policy.

The attorney general must authorize the new numbers in consultation with Congress, and that process has generally taken at least a month in the past.

But the principal drawback is funding. The United States has yet to meet the 7,000 a month quota announced in April. In May, fewer than 4,600 Indochinese refugees were admitted to this country because there was no money available to handle more.

The two supplemental appropriations measures enabling the United States to meet the 7,000 quota were tied up for some time in Congress. Though both the House and Senate have now passed them, the bills differ and must be reconciled. A conference on the subject will not take place until after July 10 because of the congressional recess.

State Department officials said that when money becomes available, they intend to make up for lost time by admitting 8,500 Indochinese refugees in July and 9,500 in August. If possible, they said, they will draw on emergency funds to increase those numbers slightly, but could not do so by as much as 7,000 a month.

The situation is further complicated by the approaching end of the budget year on Sept. 30. "At this last stage in the budget cycle, it's almost impossible to get a third supplemental appropriation," said one State Department official.

Though the private voluntary agencies that handle refugee resettlement in this country have said they have more than enough sponsors to cope with an increased flow, a voluntary agency spokesman told a House immigration subcommittee hearing on Wednesday that some "gearing-up time" was needed to take in as many as 14,000 refuges a month.

Transportation is another problem: Most refugees are flown ot the United States on regular commercial flights, which are already heavily booked by tourists during the summer.

The State Department is now concentrating its efforts on preparing amendments to the fiscal 1980 budget which goes into effect Oct. 1. State Department and Health, Education and Welfare officials estimate that added costs for the additional 7,000 refugees a month will amount to about $170 million.

Though members of Congress and senators ranging the political spectrum from Sen. Edward M. Kennedy (D-Mass.) to Sen. Bob Dole (R-Kan.) endorsed the president's move, many said that their commitment to backing it would be contingent on other nations of the world taking a greater share of responsibility for the more than 300,000 regugees now awaiting than 300,000 refugeees now awaiting Asian camps.