Pilobolus, a dance troupe with an eye-catching name (it's a mushroom fungus) and an even more eye-catching stage presence, returned to Washington last night for a week's engagement at the National Theater.

The first Pilobolus visit was on the Washington Performing Arts Society's modern dance series at Lisner last spring. The two performances were such a surprise popular success that WPAS opted for an expanded run this time. The National, once a thriving site for dance, was picked for its central, downtown location, with the thought that if Pilobolus draws well perhaps future dance attractions could be booked into this commodious house.

Founded at Dartmouth College in 1971, Pilobolus is one of the most adventurous dance groups on the current scene. The four men and two women of the troupe operate as a "collective," in respect to artistic decisions and often choreography as well. Their fascination with biomorphic imagery and their distinctive theatrical sense gives their work a thoroughly individual appearance and excitement.

Two complete programs are being offered: the first repeating tonight, Tuesday, Friday and Saturday evening; the second on Wednesday, Thursday and Saturday matinee. Each program will include a Washington premiere. For other information, call 628-3393.

The quest for roots has touched dance too, as the growing interest in historical dance styles is demonstrating. Locally, the Dupont Consortium, which has presented pre-classic dance performances hereabouts, is now expanding its training and performing activities.

Registration will begin April 18 for a 12-week course in Renaissance court dancing, to be given at two locations on Monday and Thursday evenings. No dance experience is necessary, but a background in sports, gymnastics or music will be helpful.

Later this month a course in Baroque dance will be added, to be taught by Janice Pforsich of the Juilliard and the Dance Notation Bureau faculties. The Baroque class will meet alternate Wednesdays at the Washington School of Ballet, with an eye towards the eventual formation of a performing unit. Ballet training is a desirable preparation. For additional information, call 387-6569.

Upcoming performances of note: George Washington University's annual choreographer's concert, ranging from traditional to experimental works, Friday and Saturday at 8 p.m. and Saturday at 2 p.m., Marvin Theater . . . Georgian Dancers of Israel, Friday, 8:30 p.m. at Kennedy Center Concert Hall . . . Free Association improvisatory dance group, Friday and Saturday at 8:30 p.m., Grace Church, Georgetown . . . Maryland Ballet, with special guests Natalia Makarova, Ivan Nagy, Helgi Tomasson and Anna Aragno, Sunday at 2:15 and 7:30 p.m., Lyric Theater, Baltimore . . . Choreo 18 in works by Anna Sokolow, Laura Glenn, Liz Lerman, Maida Withers and Midge Kretchmer, Sunday at 8 p.m., Jewish Community Centre, (repeats on April 23).