The Western attempt to salvage a U.N. plan for Namibian independence was kept alive today by an American offer to provide U.N. forces with electronic sensors to help monitor the territory's borders.

The "proximity talks" held here on the ministerial level recessed for at least a week to allow South Africa, the various Namibian nationalist groups and the African "front-line" states to consider a working paper on monitoring put forward by Secretary of State Cyrus Vance. They will also consider Western clarifications of the other outstanding issue, the disposition of nationalist guerrilla forces inside Namibia.

South African foreign minister Pik Botha told the Western negotiators during a 2 1/2-hour meeting this morning that he would have to take the proposals back to his government and would provide an answer in a week to 10 days, according to participants in the talks.

Some of the Western delegations seemed optimistic that the differences were now "bridgeable," as British Foreign Secretary David Owen put it.

Vance said, after briefing U.N. Secretary General Kurt Waldheim on the progress of the talks, "Yes, we're closer, but we've got a long way to go." He said negotiations would resume at the ministerial level if necessary.

Botha told reporters that there was "no change in the prospect for agreement. It is not close at hand. Severe difficulties have to be overcome."

American officials also cautioned that "the big issue remains the political will of South Africa." The differences themselves are less important than the political decision in Pretoria on whether to let the U.N. plan go through and leave the fate of the territory that has been administered by South Africa since 1920 to an electoral process outside South African control, the Americans said.

The meeting with the front-line states and the leading liberation movement, the Southwest Africa People's Organization (SWAPO), which followed the session with Botha, produced an "encouraging response," said a Canadian official. "The issues have narrowed. There is improvement."

The meetings were held under difficult circumstances.

First there was Pretoria's preoccupation with its own domestic scandal over the use of government funds to influence Western news media representatives and politicians. Second, the talks coincided with a U.N. Security Council meeting called to condemn South Africa for its recent raid against SWAPO guerrilla bases in Angola.

The Angolans, who had been instrumental in pressing SWAPO to agree to the U.N. plan for elections in Namibia, boycotted the proximity talks.

Botha refused to meet jointly with the American, French, British, West German and Canadian ministers until today, insisting that he had to devote his energies to the Security Council debate -- a debate in which he did not participate.

At this morning's long meeting with the Western five, he kept returning to South African charges that the West had backed away from various commitments to his government. Vance, according to one participant in the meeting, kept seeking to return to discussion of practical ways to overcome the differences.

Vance cautioned reporters that they should not overemphasize the U.S. offer of electronic monitoring equipment, although he admitted that it may help resolve one of the two remaining issues -- the monitoring of SWAPO forces based in the front-line states.

The West attempted to deal with the other issue -- the restriction of SWAPO guerrillas to bases inside Namibia -- by breaking it down into detailed questions that will be the subject of negotiations with the Western contact group in coming days.