In Washington, burning issues come and go with bewildering speed. But there was a modest demonstration yesterday at the White House that proved that Bolivians, at least, are not so fickle.

Exactly 100 years ago yesterday, Chilean troops launched a surprise takeover of the seacoast Bolivia had owned since "well before the Inca Empire," according to members of the Bolivia Residents Association, which sponsored the rally by several dozen Bolivians and some sympathetic American students.

This made Bolivia one half of the correct answer to the grammar school geography question, "What are the two landlocked countries of South America?" (The other is Paraguay.)

It also made Bolivians angry.

"This is the main foreign policy problem for Bolivia," said Guillermo Zavala, press attache at the Bolivian Embassy.

Yesterday's demonstrators envision, perhaps, "another Camp David," as Zavala suggested, in which President Carter sits down with the leaders of Chile and Bolivia to help Bolivia regain its window to the sea.

But Bolivians will have to show continued patience before bringing the dispute to a favorable conclusion, according to Zavala. First they need to improve their educational system, sustain their present political stability, strengthen their economy and build "a very good army," he said.

Negotiations on the seacoast issue have been fitful, at best, since 1904.

Chile did recently agree to give back some of the seacoast if Bolivia gave Chile some of its land in exchange, but Bolivia turned the offer down and last year broke off the negotiations again.

Bolivia "frustrated" the negotiations, charged Pedro Dazza, Chile's ambassador to the Organization of American States, in a speech before the OAS yesterday morning. In any case, Dazza added, "Bolivia is among the landlocked countries of the world that has the most privileged treatment with respect to free transit to the ocean."

At stake in the 63,000-square-mile costal territory that is rich in deposits of nitrate, copper and other resources, as well as Bolivian access to a seaport of its own, according to the protesters.

Yesterday's protesters expressed once again the persistence that has marked their cause: "Sooner or later," proclaimed their flyers, "Bolivia will have access to the Pacific Ocean."