A preliminary investigation of charges of racial discrimination in the Soil Conservation Service in Arkansas could lead to a full-scale probe of civil rights compliance by all Agriculture Department agencies in the state, USDA officials here have acknowledged.

The inquiry came after black farmers and a black conservation service employe at Forrest City, Walter White Jr., complained to the department that the soil-protection agency was involved in a number of discriminatory practices.

USDA officials will decide after hearing the conservation service review team's report whether to delve deeper into the charges by White and the farmers, even though the civil rights enforcement office's travel budget for investigations has been cut to zero by the Reagan administration.

Lawrence Bembry, associate director for equal opportunity, refused to confirm or deny that his travel budget had been eliminated. But he maintained that funds would be available if the department decides to look further at the Arkansas situation.

Bembry also said that if investigators go to Arkansas to look at the conservation service, they may expand their work to cover other USDA agencies such as the Farmers Home Administration and the Extension Service, which also have been targets of discrimination complaints.

Other departmental sources said that officials consider the Arkansas charges "sensitive" and "explosive" because of their potential for drawing new attention to a USDA civil rights program that has been under fire since 1982 for an alleged breakdown in enforcement.

Bembry asserted last week that, although his investigations budget is "limited," he has been able to obtain funds on a case-by-case basis to carry out the most urgent compliance reviews across the country. "It may seem awkward," he said, "but our needs have been supported."

A major complaint by the Arkansans was that conservation service officials were participating in a system that has excluded blacks and women from membership on the 76 local conservation district boards that oversee spending of federal and state funds for soil and water conservation.

According to Randy Young, director of the gubernatorially appointed state soil and water conservation commission, the 380 local board directors include one black and 12 women. He said the commission had not taken action to widen minority membership "in order not to create a sense of ill will between the districts and the state."

Each local board includes three elected members and two appointed by the commission. Young said the commission has the power to choose its own appointees, but that in most cases it simply accepts recommendations by the elected members.

Conservation service field worker White and complaining black farmers charged that the system precludes blacks from being named to the local boards and results in black residents of most counties being excluded from conservation assistance.

"Members of these boards have input on services available through SCS," White said, "and minorities could get more information if they were members of the boards. As it is now, our black communities don't know what is available."

L.T. Simes, a black attorney from Helena who was on the state commission for seven years, said he considered the situation "illegal and wrong." He said, "It is a dismal condition and it will remain so without some very strong enforcement."

Simes said that after he raised the representation issue last year, the commission adopted a resolution supporting more minority membership on the local boards. But, he added, the commission has continued to rely on recommendations from the local elected members.

He said that although he sought another term, Gov. Bill Clinton (D) refused to reappoint him in January. "I feel there was a connection between what I was doing and not getting reappointed," Simes said. "I was the first black in the history of the state to be on the commission and I was chairman last year. It was ironic that when I began to make headway I was not reappointed."