With support from Mayor Marion Barry, a D.C. City Council Committee began yesterday deliberating legislation that would take away the eligibility of several ethnic groups to qualify for lucrative city contracts reserved for minorities.

The measure, as proposed in January by the mayor, would limit contract preferences now granted Hispanics to those with origins in South and Central America and the Caribbean, eliminating those from Europe and Mexico.

It also would reserve benefits for Americans of specified ethnic heritages, apparently ruling out contracts for recent immigrants from Asia and Africa who are not U.S. citizens.

However, after formally proposing the legislation on Jan. 2, the mayor's legislative office quietly softened one of its provisions. In a Feb. 27 memo, it notified the council's Housing and Economic Development Committee that Barry "would not oppose" letting the city Minority Business Opportunity Commission (MBOC) determine the eligibility of all Hispanics on a case-by-case basis. MBOC proposed the change.

The new restrictions in the contracting program would result from a changed definition of minorities contained in a bill to continue MBOC as a permanent body. MBOC administers a program established in 1977 that is designed to channel 25 percent of all funds spent on city purchases to minority-controlled firms. Without the legislation, MBOC would go out of existence this year.

The existing definition of minorities in the 1977 law is "blacks, Hispanics, American Indians, Orientals and Eskimos." The definitioin proposed by Barry, based on a recommendation made last year by MBOC, would be "black Americans, American Indians, Oriental Americans, Americans with origins in South and Central America and the Caribbean, American Eskimos and American Aleut."

This would eliminate Mexico, which is in North America.

The revised definition to which Barry has given backhand support would include "Hispanic Americans" regardless of geographic origin, but would require that all the qualifying minorities be Americans from groups that are "economically and socially disadvantaged because of historical discrimination practiced . . . within the United States of America."

Courtland Cox, MBOC director, said the revised definition would eliminate such groups as Vietnamese, who have no history of being targets of discrimination in this country, and would let MBOC deal with all Hispanics individually.

Several witnesses from the Hispanic community criticized the mayor's original proposed language. Hector Rodriguez, a consultant of Caribbean origin, said benefits should be maintained for everyone of Spanish culture, regardless of race or nationality.