The United States has submitted its own compromise plan for a timetable leading to the withdrawal of Cuban troops from Angola in an effort to break the long deadlock between South Africa and Angola over the troops' presence.

The plan was submitted to the two sides during a visit to the region in mid-March by Assistant Secretary of State for African Affairs Chester A. Crocker, who has been spearheading the U.S. mediation effort to arrange for the independence of the South African-administered territory of Namibia.

It appears to mark a new stage in U.S. involvement in the search for an overall regional peace settlement combining the holding of U.N.-supervised elections in Namibia with the withdrawal of the estimated 25,000 Cuban troops stationed in Angola. Both South Africa and the United States have been demanding their departure, and the issue has become the main sticking point to implementation of a U.N.-sponsored plan for Namibia's independence approved in 1978.

A senior administration official said it was the first time Washington had submitted its own independent proposals to break the deadlock over the Cuban issue.

He said the more activist U.S. diplomacy represented a "major new step" by the Reagan administration to get an agreement and had been approved at the highest levels.

He also said it reflected a realization the United States would have to become more directly involved in the negotiating process if any agreement were to be reached, because South Africa and Angola were still far apart on the timing and extent of a Cuban troop withdrawal.

South Africa wants all Cuban troops to withdraw almost immediately upon the start of implementation of U.N.-supervised elections in Namibia. Angola last November publicly announced its agreement to the departure of most, but not necessarily all, of the Cubans as part of an overall Namibia settlement.

Complicating the Cuban issue is the breakdown of a U.S.-brokered agreement reached in Lusaka, Zambia, in February 1984 under which all South African troops sent into Angola to curb incursions of Namibian nationalist guerrillas based there were to be withdrawn. The South African forces halted their own withdrawal about 25 miles short of the Namibian border.

U.S. officials refused to disclose details of the proposed U.S. compromise. But it was understood to support the South African objective of getting all Cuban troops out of Angola through a phased withdrawal allowing the Angolan government time to adjust to security problems created by their departure.

State Department officials said that for the past four months Washington had sought to extract "ideas" for a compromise from the South African and Angolan governments without success.

"After four months of trying to elicit ideas, we decided to come up with our own ideas," one official said.

He said the U.S. plan was a "synthesis paper" and represented an extrapolation from the declared Angolan and South African positions regarding the Cubans and amounting to "an outline of what an agreement might look like."

The officials said the U.S. plan took no position on another delicate issue for the Angolans, namely the possible formation of a coalition government in Luanda including the opposition National Union for the Total Independence of Angola (UNITA). It has been waging a guerrilla war against the central government since Angola's independence in 1975.

They described the plan as being deliberately "neutral" toward UNITA, neither giving it any advantage nor leaving it at a distinct disadvantage as a result of the Cuban withdrawal plan.