A congressional subcommittee voted yesterday to authorize $500,000 a year in special federal grants for Washington museums, theaters and performing arts companies "of national significance."

"I think it's important for the nation that we provide a cultural base and showpiece here," said Rep. Paul Simon (D-Ill.), chairman of the postsecondary education subcommittee that reviews House authorizations for federal arts spending.

"In most large cities you have both state and local funding for the arts, corporate contributions and foundation support," Simon said. He noted that Washington's large cultural institutions do not have similar access because the federal government is the main business here.

Simon named the Washington Opera, Arena Stage, Corcoran Gallery of Art, Folger Shakespeare Library, Washington Ballet and Washington Performing Arts Society, saying these and other groups might benefit under his proposed plan.

The $500,000 would be part of the NEA budget and earmarked for Washington. Next year's proposed $125 million NEA budget is 13 percent less than last year's.

A similar plan was advanced in 1978 by Rep. Sidney Yates (D-Ill.), chairman of the House subcommittee that must appropriate arts funds after they have been authorized, but it was killed after critics argued it would distort the NEA grant-making process by channeling funds away from projects in other parts of the country and into the District of Columbia.

Yesterday's action is the first step in a long congressional approval process, and Simon said his plan is "a long way from becoming reality." He also said he has not formulated exactly how it would operate but would work out details with NEA Chairman Francis S.M. Hodsoll.

Lisa Phillips, Simon's committee aide, said grants under the plan would be "in addition to what they cultural institutions get from the NEA" regularly. However, Simon said in a telephone interview, "The aim is to help groups that are not helped in any other way."

Asked if groups already receiving NEA support could, in addition, receive money under his plan, Simon said, "If they get NEA grants that does not exclude them, but I assume that would be weighed by Hodsoll."

Hodsoll could not be reached for comment yesterday.