President Reagan stopped by a reception at Decatur House late yesterday to announce that a new foundation will honor White House press secretary James S. Brady, who was shot in the head last year in the assassination attempt on the president.

The foundation is being established to aid anyone wounded in an assassination attempt on any senior federal official or presidential candidate. The foundation is also authorized to establish scholarships as a memorial to victims of assassination attempts.

Former Office of Management and Budget director James T. Lynn has been named president of the foundation, former Democratic National Committee chairman Robert Strauss is to be a fund-raising cochairman. Board members include journalists and business executives.

Brady, who undergoes daily therapy under the supervision of George Washington University Hospital, was unable to attend the reception. Reagan recalled, however, how Brady threw out the first ball at the Old Timers Classic at RFK stadium Monday night.

When Brady, in a wheelchair, appeared on the field to hurl a ball sure and straight, he was greeted with cheers louder and more sustained than any given to the former baseball stars playing in the game.

Reagan said the appearance also proved that Brady had "high connections": "It was raining and he was introduced and it stopped raining."

Brady, who has speech problems and some paralysis on his left side, is still the official White House press secretary. His physicians say they do not know when he will be able to return to any form of work.

Earlier in the day, Reagan boasted to Hispanic supporters and appointees invited to the White House that his administration had brought Hispanic Americans "onto the White House staff as never before." He said he had appointed 17 Hispanics to policy-making positions in his first year in office--nearly twice Carter's record, he said--and he singled out eight by name.

"But let me point out," he added. "These Hispanic members of the administration are not picked because of their ethnic background. They were chosen because they are skilled, intelligent people who have a contribution to make. They just happened to be the best people for the jobs that we asked them to do."

Appealing for their support in the "tough battle" in Hispanic communities in the coming elections, Reagan said it was widely recognized that Hispanics are in tune with his administration's philosophical emphasis on restoring a strong sense of community and family. And, because so many Hispanics feel strongly about parochial schools, he said, his proposal for tuition tax credits has a "natural appeal."

Meanwhile, Reagan signed legislation curtailing taxpayer subsidies for tobacco growers. The bill is intended as a step toward ending the Treasury's responsibility for tobacco supports, which have cost $600 million over the past five decades.