The Hirshhorn Museum and Sculpture Garden yesterday announced new acquisitions valued at perhaps $2 million.

Three important pieces -- a seven-foot-high sculpture by the late Gaston Lachaise, a Richard Estes streetscape completed late last year, and a 1967 painting by the Spaniard Joan Miro -- have been bought by the museum.

The Hirshhorn also has received two large-scale gifts. One, consisting of 41 contemporary paintings and sculpture, comes from David Anderson of Buffalo, N.Y., whose mother, the late Martha Jackson, was a well-known New York dealer. The other donation, from Joseph J. Hirshhorn, the museum's founder, includes 14 Benin bronzes and 28 contemporary sculptures.

"Standing Woman (Heroic Woman)" of 1932 is perhaps the best-known bronze of Gaston Lachaise. Though the sculptor died in 1935, a new cast of his statue is being made for the museum. Purchased for a price said to be between $200,000 and $250,000, it will go on view in June. The Miro, "Woman Before an Eclipse with Her Hair Disheveled by the Wind," cost between $400,000 and $450,000. Bought from Pierre Matisse, the Manhattan dealer, it was recently displayed in a Hirshhorn exhibition devoted to the work of the 88-year-old artist. A Smithsonian Institution program for buying its museums "outstanding" works of art that cost more than $200,000 each provided half the monies. Matching funds were raised by the Hirshhorn's 10 trustees.

The new Estes, "Waverly Place," cost between $100,000 and $150,000.

The Anderson gift includes works by 17 contemporary artists, among them Sam Francis, Joan Mitchell, James Brooks, John Chamberlain, Bob Thompson, and Alma Thomas, the late Washington color painter. The 14 Benin bronzes donated by Hirshhorn bring to 35 the number of castings from that Nigerian city-kingdom that he's given the museum. Contemporary sculptures by such artists as Beverly Pepper, Kenneth Snelson, Isaac Witkin and Jack Zajack also were included in his latest gift. Abram Lerner, the museum's director, yesterday estimated the value of the Anderson and Hirshhorn donations at "well in excess of $1 million."

The museum owned some 6,000 works of art when it opened to the public in 1974.Since then it has acquired more than 1,000 additional pieces, most of them through gifts. Of these, more than 400 have come from Joseph Hirshhorn. Other major gifts include a set of 114 Saul Baizermans, given by his widow in 1979, 67 drawings by the poet e. e. cummings, donated anonymously in 1976, and five pictures, four paintings and a drawing, by Washington's Gene Davis, gifts from Washington professor Donald Wall.