The White House said Wednesday President Reagan still stands by his "Star Wars" anti-missile program despite a congressional study that says its electronic brains would be so large and complex that there is a "significant probability" they would fail.

White House spokesman Marlin Fitzwater said Reagan has not been briefed on the study.Nevertheless, Fitzwater said, "Suffice to say the president still believes in the Strategic Defense Initiative program. He believes in its potential and certainly has no plans to change our policy or our priority status for SDI."

The study's harshest criticism was reserved for the computer systems which would be needed for "battle management," the Pentagon term for tracking and targeting Soviet missiles.

"In OTA's judgment, there would be a significant probability (.e., one large enough to take seriously) that the first (nd presumably only) time the BMD system were used in a real war, it would suffer a catastrophic failure," said the report. BMD stands for ballistic missile defense.