Nearly 2,000 employes at World Bank headquarters at 19th and H streets NW., representing about 40 percent of the workforce, walked off their jobs for three hours yesterday and staged a quiet sit-in demonstration in an outer courtyard to protest salary proposals.

Across 19th Street at the International Monetary Fund, several hundred employes staged a simultaneous demonstration by sitting down in the area of the front entrance, a spokesman said.

An organization of nonprofessional wokrers called the demonstrations, asserting that proposals for determining salary increases discriminate against such employes as secretaries, clerks and messengers. The World Bank employes about 5,000 people at its Washington headquarters, and the IMF has a staff of 1,500 here.

The demonstrations came on the eve of a meeting of the governing board of the IMF at which the proposals will be discussed, officials said. The comparable unit for the Bank will discuss the issue sometime in the future.

Spokesmen for both international organizations and for groups that represent employes refused to divulge details of the proposals.

Other sources said, however, that the proposals recommend supplanting the system that gives the same percentage salary increase to all employes with one that gives larger increases to professional staffs.

The proposals are said to recommend that professional employes receive salaries comparable to workers in similar jobs in France, Germany and the United States. Nonprofessional would receive salaries comparable to their American counterparts in the private sector. Opponents of the proposal said this would work unfairly against the nonprofessional group.