The president-elect of the Dominican Republic expressed strong support yesterday for President Reagan's initiative to spur foreign investment and development in Caribbean countries, but he suggested that those efforts could be undercut by the U.S. decision to restrict sugar imports.

Salvador Jorge Blanco, who takes office next month, met briefly with Reagan at the White House and the two posed for photographs in the Rose Garden.

After the meeting, Blanco told reporters that his country faces the "most acute economic crisis in 50 years" because of a worldwide depression in sugar prices, high energy costs and the U.S. import limits.

He said that while he hoped the Caribbean Basin Initiative could become law, "no initiative to help the Caribbean can succeed if it coincides with a violent deterioration in the terms of trade of the region."

After Blanco's "working visit" with Reagan, he went to Capitol Hill to lobby for the Caribbean Basin Initiative, following a pattern set by Honduran President Roberto Suazo Cordova, who met with Reagan on Wednesday.

White House aides said the back-to-back visits of the two Caribbean heads of state with stepped-up efforts to win congressional support for the Caribbean aid plan was a coincidence.

But they acknowledged that this week they had intensified their efforts to gain congressional support for the plan, making it one of their top legislative priorities. Top domestic and foreign policy aides are involved in the effort to get it passed.

The sudden urgent efforts on behalf of the plan, Reagan's first major foreign policy initiative, were the result of his frustration at seeing it languish on the Hill. Aides also acknowledged that its success could help improve relations with Latin countries unhappy with U.S. support of Great Britain in the Falklands war, and they did not deny that there was potential domestic political benefit.

About 200 of Reagan's Hispanic political supporters are being brought to the White House next Tuesday to be briefed on the initiative by U.N. Ambassador Jeane J. Kirkpatrick and other administration officials.

The next day, Reagan and the First Lady are expected to attend what is described as a "gala Caribbean summer evening" at the Organization of American States. The event is being sponsored by a group called "The CBI Coalition," which lists Eastern Airlines chairman Frank Borman and former Chase Manhattan Bank chairman David Rockefeller as two of its leaders.

Reagan unveiled the Caribbean Basin Initiative, a proposal he had talked often about during the election campaign, last February in a speech warning of the danger that "new Cubas" will arise from "the ruins of today's conflicts" without an initiative to deal with the poverty and social inequality in the Caribbean basin.

Overshadowed on the Hill all spring by the battles over the budget, the plan nevertheless drew strong opposition from business and labor who feared that its emphasis on shoring up Caribbean economies by eliminating most tariffs would hurt American businesses and workers.

Besides El Salvador, the Dominican Republican and Honduras, the bill provides assistance to Costa Rica, Jamaica, Haiti, Belize and Guatemala.

Those countries have labored on the measure's behalf, sending government officials, rum and sugar producers and others to the Hill to lobby.

But there are misgivings, a feeling that the amount of aid is too little and, as one island-country diplomat put it delicately yesterday, "inconsistency" in talking of aiding the Caribbean countries by opening up U.S. markets on the one hand and then sharply limiting one of their major exports, sugar, on the other.

On another matter, Reagan called in his Cabinet members to try to resolve policy differences within the administration on grain sales to the Soviet Union.

White House officials privately predicted Reagan would listen to the arguments and decide early next week whether to let the current pact lapse when it expires Sept. 30, extend it for a year, or negotiate a new accord.

The Cabinet session followed a meeting between the president and House Agriculture Committee members.