President Carter announced tonight that the United States will double the number of Indochinese refugees it accepts as part of a seven-nation commitment reached here to increase significantly the flow of aid to the homeless boat people of Southwest Asia.

Less than two hours after the leaders of the industrial democracies jointly pledged to do more to help the refugees Carter became the first to act, doubling the monthly quota of refugees settled in the United States to 14,000.

The president's quick move was designed to spur the other leaders to take equally dramatic action to live up to the general commitment reached at the Tokyo economic summit conference.

The officials expressed hope that the higher quotas could be assigned starting next monh. Current arrivals of refugees in the United States actually have not yet caught up with the current quotas. Officials in Washington said, however, that the increase is not likely to take effect until October at the earliest. [Details, A26].

Eventually, Congress would have to appropriate the funds necessary to double the program.

Administration officials here estimated that Carter's action will cost about $150 million a year above the $200 million a year already spent in resettling the refugees. The increased U.S. commitment is for a year, after which it will be reviewed, they said.

None of the other summit nations immediately announced specific increases in the number of refugees it will accept or the amount of money it will contribute to the international resettlement effort, although all seven nations pledged to do more in both areas.

U.S. officials pronounced themselves satisfied with the joint commitment of the seven nations while pointedly urging reporters to measure what the others eventually do against Carter'ss announcement tonight. "This is basically what we sought," one U.S. official said.

Largely at the president's instigation, the plight of the more than 300,000 Indochinese refugees became second only to energy among the issues discussed today at the economic summit conference of the United States and its principal allies - Japan, Canada, Britain, France, West Germany and Italy. By agreement reached earlier this week in Tokyo, the United States and Japan took the initiative leading to tonight's joint statement pledging the significant increase in aid.

Asserting that the plight of the refugees "poses a humanitarian problem of historia proportions and constitutes a threat to the peace and stability of Southeast Asia," the seven leaders called on the governments of Vietnam and other countries in Southeast Asia "to take urgent and effective measures so that the present human hardship and suffering are eliminated.

"The governments represented will, as part of an international effort, significantly increase their contribution to Indochinese refugee relief and resettlement by making more funds available and by admitting more people, while taking into account the existing social and economic circumstances in each of their countries," the joint declaration said.

The seven leaders also asked U.N. Secretary General Kurt Waldheim to convene an international conference on the refugee question and pledged their "full support" for the effort. Such a conference was already in the planning stages and is now tentatively scheduled for early next month in Geneva.

The next step in the process of dealing with the refugee problem will take place Sunday and Monday, when Secretary of State Cryrus R. Vance takes the results of the Tokyo summit to a five-nation foreign ministers meeting of Southeast Asian nations in Bali.

In a sense, the U.S. initiative at the summit was an attempt to buy time in the effort to avert even greater tragedies for the boat people. Last week, Vance dispatched messages to the Southeast Asian countries asking them to await the results of the Tokyo summit before taking any further actions against the refugees who are flooding into their countries and producing great internal political stress.

In recent weeks, Thailand evicted 42,000 Cambodian refugees and Malaysia took steps to force newly arrived refugees away from its east coast. They are reacting to a dramatic rise in the number of refugees. More than 59,000 boat people, the bulk of them from Vietnam, entered nearby countries in May.

Moreover, according to U.S. officials, it is estimated that 30 to 50 percent of the refugees expelled never reach safety and drown in the South China Sea.Ships of the U.S. 7th Fleet are under standing orders to repair refugee boats or to pick up passengers from sinking boats and take them to safety, the officials said.

Before tonight's announcement, U.S. officials cabled the Thai and Malaysian governments, telling them the summit declaration was "a direct response to the crisis" they face. The officials said the reaction was extremely positive.

Initial reaction from Bali, however, was less enthusiastic.

American officials have drawn a parallel between Vietnam's actions and Germany's treatment of German Jews in the late 1930s that eventually led to the mass executions of the 1940s. The United States has urged its allies to exert pressure on Vietnam to halt the forced exodus and, at Carter's orders, last week took the issue directly to Vietnamese authrorities at the United Nations in New York, officials said.

The president's decision to double the monthly flow of refugees to the United States is not likely to be popular with blacks, hispanics and other groups that traditionally tend to vote Democratic but may consider the new arrivals a threat to jobs. But in his announcement of the decision, relayed to reporters by a White House official, Carter appealed to the "traditional compassion" of Americans in seeking support for the decision.

"We are prepared to act with the compassion that has traditionally characterized the United States when confronted with such situations of human crisis," he said. "Thousands of human lives are at stake. Accordingly, I have decided to increase admissions of Indochinese refugees in the coming year from 7,000 per month to 14,000 per month.

"The response of Americans to the plight of refugees has always been generous," Carter continued. "I am confident that we can count upon a similarly generous reponse to the present challenge. We can and will work together to find homes and jobs for the Indochinese."

Prior to the summit, U.S. officials had talked of increasing the monthly quota to 10,000 refugees. In going to 14,000, the president complied with a request of the U.N. High Commissioner for Refugees that key nations double their quotas. The U.S. action indirectly put pressure on the summit partners to do the same.