Black conservatives struggled yesterday to breathe life into their fledgling organization, two years after boasting that they were so in tune with mainstream black thinking that they would build a new movement to rival the National Association for the Advancement of Colored People.

Yesterday, Clarence Pendleton, president of the Reagan administration-inspired New Coalition for Economic and Social Change, conceded that the group had gotten off to a slow start.

Only about 300 members have been recruited, and chapters have been formed only in Washington, Oakland and Chicago since the group first met in San Francisco in December, 1980.

"There's been a hiatus," Pendleton said. "We want to find out where we're going to go, how we're going to get there and who and what can help us and who and what can hurt us."

The conservative Heritage Foundation paid for yesterday's conference, entitled "Rethinking the Black Agenda," at the Hyatt Regency in Crystal City.

Participants spoke against affirmative action, government regulation and the minimum wage and in favor of strategies to promote black economic development and provide alternatives to public schools. The arguments were much the same as those raised two years ago in San Francisco.

A few had more provocative proposals.

For example, William Keyes of the Department of Education, said it was his view that children ought to be able to quit school and go to work if they desire, although he was unwilling to say at what age he would be willing to permit them to do so.

Walter Williams, an economics professor at George Mason University, after complaining that crime plagued inner-city businesses, said, "I would suggest vigilanteeism as the last resort if the police are not going to help."

Others at the conference later disassociated themselves from this view.

White House Counselor Edwin Meese III told the group that its goals coincided with those of President Reagan, and he promised a more frequent dialogue with blacks on administration plans for the next two years of Reagan's term.

"The ideas you have expressed here, that there are alternatives to increasing government spending, social programs and government oppression, should and will be reflected in the policy decisions we make," Meese said.

Despite problems in building a grass-roots movement, members of the group have been successful in obtaining appointments in the Reagan administration. Pendleton has been named chairman of the U.S. Commission on Civil Rights and at least six others have posts in the administration or serve on advisory boards.

The group has also been successful in tapping funds from white conservative groups such as the Heritage Foundation. Pendleton said that all but about $20,000 of the $220,000 the group has raised has come from such conservative corporate and foundation sponsors as the Coors brewery, Getty Oil and the Olin and Scaife foundations.

Pendleton said the group received the contributions after going to the sponsors and saying "we have similar philosophies." He was undeterred when Willa Johnson, senior vice president of Heritage, suggested that they might be criticized for cosponsoring a conference with the Heritage Foundation, a group, she said, that is "No. 1 white and No. 2 unabashedly conservative."

Heritage officials stressed during the conference that their conservatism does not mean they are uncaring or insensitive to the problems of blacks and other minorities.