President Reagan obviously hoped to do himself some political good by meeting with Hispanics and Republican congresswomen yesterday, but he suffered a small political embarrassment when the Hispanics, arriving at the White House to show their support for him, were forced to enter through a metal detector erected in front of the West Wing especially for their visit.

Larry Speakes, Reagan's spokesman, said two of the president's aides, chief of staff James A. Baker III and deputy chief of staff Michael K. Deaver, asked the Secret Service "for some answers" about the unusual added security precautions taken for the Hispanics.

The Reagan administration is careful to try to avoid any appearance of unfair treatment of minority groups, particularly Hispanics and blacks, who have been critical of the effect budget cuts have had on the poor and disadvantaged.

Despite the fears of Reagan's aides that the minority group might take umbrage at being singled out as a higher than normal security risk, Tirso del Junco, California state GOP chairman and president of the Republican National Committee's Republican Hispanic Council, said he was "not offended."

"I've been through security checks so many times at so many dinners," he said. "This is usually customary, and I believe it is right and proper to take all kinds of security precautions."

Also yesterday, the president met with a group of Republican congresswomen who wrote to him in February to complain that his policies were viewed as harmful to women and to urge him, despite his opposition to the Equal Rights Amendment, to stay out of any effort in Congress to pass a new ERA.

After meeting with the president, Rep. Lynn M. Martin (R-Ill.) said Reagan made no promises but listened to their expressions of concern that their party is being hurt by the perception that he is an opponent of women.

She said the meeting is the first of a series with the president to develop an administration agenda for initiatives on issues of concern to women.