President Reagan, responding to a letter from former Austrian chancellor Bruno Kreisky calling for more flexibility in arms control talks in Geneva, said that "Soviet intransigence" is stalling the negotiations.

In a letter released yesterday replying to Kreisky's request that Reagan reconsider this country's December deadline for an agreement, Reagan wrote that any delay in deployment of Pershing II and cruise missiles in western Europe would weaken the allies' bargaining position.

"A delay in our deployments would only encourage the Soviets to believe that NATO's resolve was faltering and that they could stretch our negotiations endlessly without addressing our legitimate security concerns," the president wrote.

Kreisky wrote Reagan Aug. 10, asking him to consider a delay in placing missiles in Europe to match the Soviet missiles aimed at the continent. He cautioned the president that sticking with the December deadline would endanger public support for the United States in Europe and might force the Soviets to abandon the Geneva talks.

"If no results are reached by the deadline you have set," the former prime minister wrote, "do prolong the negotiating period for another few months, and reasonable people throughout the world will understand that you seek to get a result. There is no sense in upholding prestige while letting negotiations founder . . . .

"What is at stake is the relationship of a major part of Europe's young generation to democracy, and I appeal to you, Mr. President, to attribute just value to this stake," Kreisky wrote in a letter he released to the press. "It will be of decisive and profound importance to the relations between our democracies, the European and the American one."

Reagan, in response, said that while he wants "solidarity among the democracies," the Soviet downing of the South Korean jetliner with a loss of 269 lives two weeks ago is an example of a "totalitarian system."

He added that he doubted that "the relationship of European youth to their democratic systems is as tenous as you suggest . . . . Young people in both Europe and the U.S. and elsewhere respect both the responsibilities as well as the privileges of democracy."

Meanwhile, Reagan wound up a week of activities for Hispanic Americans with a speech in the Rose Garden to Hispanic veterans. During the speech, he unveiled a stamp to commemorate the valor of Hispanic Americans in war.

"Among your number," the president said, "have been the first American flier to be shot down over Vietnam; the first American to escape from captivity in Vietnam and make his way to freedom through communist-infested territory; the last Marine to leave Saigon . . . . And by the way, in case you haven't heard, at our request, the United States Postal Service will be issuing a commemorative stamp in honor of this enormous and awe-inspiring record."

The speech ended what administration officials said was a "spectacular" effort to attract Hispanic voters to a possible Reagan reelection effort as well as to the Republican Party. White House officials said they now plan to add other events to appeal to Hispanic voters.

Also yesterday, Reagan met with 26 supporters of legislation to provide tuition tax credits to parents of children in private schools. Earlier in the week, Reagan telephoned Senate Finance Committee Chairman Robert J. Dole (R-Kan.) and Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) to discuss strategy for getting the credits to a vote in the Senate. The proposal has been approved by the Finance Committee.

Administration officials denied speculation in Congress that the president would consider a trade-off in which the White House would support a tax increase if the Congress approves tuition tax credits.