BEIRUT - Indirect negotiations to resolve a maritime border dispute between Lebanon and Israel will be bolstered by a proposal Lebanese officials presented to a U.S. mediator in Beirut on Tuesday, Washington's envoy said.

"I think that it will enable negotiations to go forward," mediator Amos Hochstein said in an interview with U.S.-based Al-Hurra TV, responding to a question about the Lebanese government's position.

Hochstein landed in Beirut on Monday at the invitation of Lebanon's government, which had objected to the arrival of a vessel operated by London-based Energean (ENOG.L) off the Mediterranean coast on June 5 to develop a gas field known as Karish.

Israel says Karish is in its exclusive economic zone, but Lebanon says the field is in contested waters and should not be developed until the two countries conclude talks to delineate their maritime boundary.

"We're in a delicate place to try to get the sides to narrow the gaps and get to a place where they can reach an agreement," Hochstein said after meetings with Lebanon's president, parliament speaker and caretaker prime minister.

"I think that's crucial for Lebanon and quite frankly crucial for Israel," he said, adding he would take Lebanon's proposal to Israeli officials and then circle back to Lebanese authorities once he had a response.

Maritime boundary talks hit an impasse last year when Lebanon expanded its claim further south from a boundary known as "Line 23" to "Line 29," adding around 1,400 square km (540 square miles), including part of Karish.

Hochstein suggested a line that would create an S-shaped boundary - partly along Line 23, and partly to the north of it - instead of a straight line, but Lebanon did not officially agree to the proposal.

The proposal would have given all of Karish to Israel and most of the so-called Qana prospect - an area with the potential for a commercially-viable gas find - to Lebanon.

Lebanese officials were going instead to ask for Line 23 plus a bit more to the south, three Lebanese officials with knowledge of the talks told Reuters on Monday.

(Reporting by Timour Azhari and Maya Gebeily; Writing by Timour Azhari; Editing by Frank Jack Daniel and Mark Heinrich)