The D.C. Office of Human Rights announced yesterday that it found preliminary evidence that elan, a chic restaurant and drinking spot in the heart of Washington's burgeoning K Street office area, has engaged in illegal discriminatory practices against blacks.

Anita Bellamy Shelton, director of the office, said she referred the case to the city's 15-member Human Rights Commission for a final decision and possible penalties. Commission Chairman Charles Morgan said he would schedule a hearing.

Cases against elan and four other popular night spots were initiated by the Office of Human Rights last year after The Washington Post reported that white-owned establishments were restricting the admission of blacks by imposing apparent racial quotas, admission card requirements and dress codes. The use of such practices to discriminate racially would violate the city's 1977 Human Rights Act.

The Post report was based on investigation and inverviews with dozens of persons including Effi Barry, the wife of the mayor, who said blacks often were denied admission to some downtown nightclubs.

Shelton said two clubs cited for discrimination, the Apple Tree and Plum Discotheque, signed conciliation agreements requiring nondiscriminatory admissions and affirmative action in hiring. She said two other clubs, Phase One and Lost and Found, still are under investigation.

Shelton said elan's application of its requirements for cards or prepaid admissions by patrons resulted in restricting entry on the base of race and sex. She also said elan apparently violated the law by failing to provide information sought during the office's investigation.

Barry Silverman, general manager of elan, said there has been no discrimination of any kind since he took over that job five months ago. Silverman said the previous management did not maintain records of the racial compositions of the patrons that was sought by the Office of Human Rights during the period in which discrimination was alleged.