The State Department yesterday said it is considering a request from Venezuela for detailed data about possible purchase of advanced F16 jet fighters, a step that would end the longstanding U.S. ban on introducing sophisticated weaponry such as supersonic jets into Latin America.

Spokesman Dean Fischer stressed that Venezuela wants the information "to provide the basis to make an informed decision" about whether to go ahead with a formal request to buy the planes.

Fischer added that the Reagan administration has not decided to sell the planes, but he conceded that the United States would not be entertaining the request for information if it intended to bar the sale.

The United States, he said, considers Venezuela a key democratic country in northern Latin America, and has "a strong interest" in helping Venezuela meet its defense needs.

The administration is understood to be especially anxious to make a gesture toward President Luis Herrera Campins' government because it has strongly supported U.S. efforts to bolster President Jose Napoleon Duarte in El Salvador.

The administration also hopes that Venezuela, with its oil wealth and influence in Latin America democratic circles, will play a leading role in U.S. efforts to foster greater pro-western cooperation among Caribbean nations.

In addition, the administration already has announced its intention to scrap former president Jimmy Carter's policy of barring transfer of sophisticated weaponry to sensitive Third World areas and to use arms sales instead as a tool to help friendly countries in regions such as the Caribbean. The administration says it believes there is a danger of spreading communist influence and subversion in that area.

The question of selling advanced military jets to Latin America has been a sensitive subject in U.S. relations with the region for almost 20 years. In the face of past U.S. efforts to keep supersonic jets out of the area, many Latin American countries have turned to other suppliers for such planes.Venezuela, for example, has French Mirage jets.

U.S. officials said privately that the Venezuelans are tentatively interested in buying approximately 20 F16s, a single-engine plane capable of firing missiles. Although full details are not available, Venezuela's interest is understood to center on a relatively simple version of the plane being developed for use by smaller air forces.

Fischer also announced yesterday that Chilean Foreign Minister Rene Rojas will arrive here Monday for a visit that is to include talks with Secretary of State Alexander M. Haig Jr. and Vice President Bush.

The visit is part of the administration's campaign to improve relations with the military regime of President Augusto Pinochet after a long period of strain caused by the Carter administration's opposition to Chilean human rights violations and alleged official Chilean complicity in the 1976 murder here of exiled Chilean diplomat Orlando Letelier.

One of the new administration's earliest actions was to lift two of the sanctions imposed under Carter because of Chile's refusal to extradite two officers under indictment here in the Letelier case.

In a speech to a group of businessmen yesterday, Thomas O. Enders, assistant secretary of state-designate for inter-American affairs, reiterated that the administration's goal is "more normal relations" with Chile, and he indicated that remaining sanctions are likely to be removed soon.