The second shake-up in a year has rattled the real estate lending division of Riggs National Corp., parent of Riggs National Bank, which lost $56.6 million in 1990 because of bad real estate loans.

William H. Stevens, Riggs senior vice president in charge of real estate loans, was fired Monday because of personality conflicts and disappointment over the worsening condition of the loan portfolio, according to Riggs employees who asked not to be identified.

Stevens, who could not be reached for comment, took charge of the bank's real estate loans in March. He replaced Robert E. Pickeral, who was fired at the end of 1989 because of loan problems that surfaced as a result of the slumping real estate market.

Riggs spokesman David Palombi confirmed that Stevens is no longer with the company but he declined to comment on the circumstances surrounding his departure.

Riggs employees said that Stevens spent his nine months on the job trying to rid the bank of its problem real estate loans but was unable to put the bank's mounting troubles in check.

At the end of 1990, loans that were no longer paying interest or were in default totaled $158.8 million, a large increase from the $4.5 million in troubled loans on the books in 1989.

In December, regulators from the federal Office of the Comptroller of the Currency, which oversees national banks, told Riggs that more precautions were necessary to protect against future losses.

Following the regulators' review, Riggs added $81.9 million to the reserve that protects against past and future loan losses. Riggs said it expects most of those losses to come from its commercial real estate loan portfolio.

Riggs Chairman Joe L. Allbritton said late last month that Riggs "is aggressively dealing with this situation" and hopes to return to profitability in this quarter.

Stevens, who spent 20 years at Chemical Bank before coming to Riggs, clashed with management over how to resolve troubled loans, according to employees.

According to Riggs sources, Allbritton was frustrated with Stevens's performance and assigned another banker a few months ago to help Stevens oversee the real estate division. The second banker, Delbert Stewart, will now take over the job, the sources said.