A former official of the Social Security Administration pleaded guilty today to conspiring to solicit a $280,000 bribe from a Greenbelt computer software firm.

Herbert Derian of Crownsville, who worked as a GS-15 computer specialist in the deputy commissioner's office at Social Security headquarters, admitted to seeking a bribe from the chairman of OAO Corp., a software and engineering company.

OAO Chairman Cecile Barker contacted the U.S. attorney's office and reported that Derian approached him and asked for a bribe. Barker cooperated with FBI agents in a lengthy undercover investigation.

In January, Kenneth M. Barry, director of Social Security's software technology center here, was convicted in a bribery scheme in which he was accused of soliciting more than $400,000 from a California computer software firm in exchange for helping the company get a $4 million Social Security contract.

In accepting a plea agreement, Derian agreed to cooperate with government. FBI officials would not comment on whether an investigation of Social Security computer contracts is continuing.

A spokesman for the Social Security Administration was unable to supply information about Derian's salary or duties at the agency. He said Derian went to work at SSA in 1981 and resigned in July.

In documents presented in court today, the government charged that in 1983, Derian approached Barker and told him that he could arrange for OAO to be awarded a $7 million contract to supply computer software if Barker paid him $280,000. Barker reported the bribe attempt to the U.S. attorney's office.

Barker used funds supplied by the FBI to pay Derian $9,000 as the first installment on the $280,000, according to a statement released by the FBI and the U.S. attorney's office here. The FBI spent about two years investigating the case.

Derian faces a maximum penalty of five years in prison and a fine of $10,000. However, prosecutors recommended a jail term of one year in exchange for his guilty plea.