The 350,000-member plumbers and pipe fitters union said yesterday that it has banned foreign cars from the employe parking lot of its national headquarters here, joining a small but growing number of unions in symbolic protests against foreign imports that eliminate American jobs.

"The time has come to put an end to mere lip-service support for our brothers and sisters in the labor movement whose jobs have been lost, either directly or indirectly, by the rising tide of foreign imports," Marvin J. Boede, president of the United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry, said in a statement explaining the ban.

Free parking in the union's 70-car employe lot at 901 Massachusetts Ave. NW will be "limited to those who drive cars that have been built by American workers," Boede said. The ban will actually affect only about eight employes who drive foreign cars, and some of them agree with the ban, a union spokesman said.

Others, however, are upset at the action and have protested to their union, the Office and Professional Employees, which represents the plumbers' office staff. OPEIU officials were not available for comment.

The ban was prompted by President Reagan's decision to end on March 31 the "voluntary restraint agreement" that had limited Japanese auto imports, an action that Boede said "convinces us that the government is prepared to sacrifice even more jobs." Expiration of the restraint agreement is expected to result in the loss of up to 200,000 jobs in automobiles and related industries, the AFL-CIO estimates.

The AFL-CIO's "union label" department, which promotes products produced with union labor, said a handful of international and local unions have enacted similar parking bans. The United Auto Workers posted a sign at its Detroit headquarters several years ago saying, "There are 300,000 automobile workers out of work. Park your foreign car in Tokyo."