The Carter administration was told yesterday that the country's growing Hispanic population wants more federal help and sympathy - soon.

Without much help, officials of the National Council of La Raza said, frustrations in Mexican-American communities could lead to violence.

"The recent riot in Houston was an example of people feeling their needs not being responded to. They were angry and they were expressing their anger." said Raul Yzaguirre, president of the NCLR.

Yzaguirre and other council officers, speaking at the close of NCLR's first convention here, said many Hispanics are increasingly disturbed by what they regard as President Carter's failure to respond to their needs.

Dr. Marta Sotomayor, head of the NCLR board, said it is "misleading" for the administration to talk of being more responsive to Mexican Americans than its predecessors.

NCLR, largest of the Hispanic community organizations, with 100 affiliates claiming links to about 1 million Mexican Americans, said that Carter could act in two ways:

By immediately convening a White House conference on Hispanics to deal with problems from employment to education. "If we get no response," Sotomayor said, "we will call one for ourselves."

By providing assurances that the 1980 census will accurately count Hispanics. NCLR believes they may be undercounted by as much as 40 percent currently.

"We suffer politically because of apportionment and we lose out on a fair share of federal money that might be going to Hispanic communities because of inaccurate census data," Yzaguirre said.

He said an accurate census would show "at least" 18 million Hispanics - exclusive of residents of Puerto Rico and illegal aliens - rather than the 12 million figure now used by the government.

NCLR officials said Carter could, without awaiting a White House conference or new legislation, take a number of quick steps to deal with other Hispanic problems.

For example, Yzaguirre said, the president, "by the stroke of his pen," could channel as much as $350 million into bilingual education programs under Title I of the Elementary and Secondary Education Act.

As another example, he said the president could direct the Department of Labor to take steps to count unemployment among Hispanics more accurately - another area in which NCLR believes serious and undercounting occurs.

Yzaguirre said the appointment of more Hispanics to policymaking federal jobs could better "determine the direction of the federal dollar" to Mexican Americans. He said it is "atrocious" that the Labor Department for instance, "has not a single high-level Hispanic."

He cited another case - the Department of Energy. "The DOE is a new agency, starting from scratch, yet it lags way behind in terms of Hispanic employment," he said.

NCLR also urged Carter to take a more active role in the administration of justice.

Sotomayor said "there have been enough investigations" of alleged police brutality - NCLR has documented 150 cases in the last two years. She said the Justice Department should become tougher in dealing with local authorities.