RIO VISTA, Calif. (AP) _ As rescue money ran low and frustration ran high, Humphrey the wayward whale flapped and splashed in inland waters Tuesday, eluding rescuers trying to attach a space-age transmitter.

On the animal's 16th day away from his salty deep-sea home, beleaguered marine scientists gave the beast a rest from the pipe-banging, whale-chasing flotillas launched repeatedly to drive the 40-foot mammal back to the Pacific.

Those hoping to guide him through the Golden Gate did try, again, to tag the 45-ton humpback with a transmitter that would let them keep tabs on his whereabouts, but they failed, as they had in an earlier effort.

''It was a little too windy for that, so they disbanded for the day,'' said Coast Guard Boatsmate Randy Keviny.

Despite hours of work and $50,000 in expenses, exasperated experts have seen Humphrey heading toward the open sea several times, only to watch him make an unexpected turnaround and spout his way back inland through the meandering Sacramento River. Humpback whales are an endangered species.

''Humphrey needs a rest. And if he's not tired, this whole operation is tired,'' said state Sen. John Garamendi.

The special radio transmitter is designed to enable scientists to track Humphrey's mysterious course by sending signals to a National Oceanic and Atmospheric Administration satellite, on to an Arizona control center, and over to the whale team.

In keeping with the frustrating record of the overall rescue effort, just getting the device to the scene Monday wasn't easy.

The transmitter, developed by Oregon State University marine mammalogist Bruce Mate, must be jabbed into the whale with darts at the end of a 16-foot pole, said Jim Slawson of the National Marine Fisheries Service. Officials couldn't fit the pole in a plane, and a truck dispatched to deliver it broke down 25 miles from Rio Vista, Slawson said.

Humphrey was elusive Tuesday as he frolicked near sunny but windy Decker Island, about three miles south of the Rio Vista Bridge, still 50 miles northeast of the Golden Gate Bridge, under which he swam Oct. 11 on his inland odyssey.

Some scientists speculate Humphrey is defining his territory with his back- and-forth cruises. ''We're hopeful we've taught the whale he can swim south,'' said James Lecky, a Marine Fisheries Service biologist.

Future rescue steps remained almost as murky as the brackish Sacramento-San Joaquin River Delta water, following word that state and federal funds set aside for Humphrey's salvation had been spent.

Officials have said they may turn to Navy or Army vessels equipped with sonar to trail the whale as they try to direct him back along the river to the San Fransisco bay.

Garamendi, urged into rescue operation after lobbying by his five children, has called experts to convene in Sacramento on Thursday to review the situation. The Legislature's Joint Committee on Science and Technology will pay the bill, he said.

Meanwhile, Humphrey's health is uncertain in the area previously best known for houseboating and fishing for sturgeon and striped bass.

''He's very healthy. He's just swimming around and he's got great speed,'' said Garamendi aide Nona Pasquil.

Asked about earlier reports that the whale has been plagued by skin blisters and eye infections, Slawson said no one really knows how the whale is holding up.

''I'm not sure that anybody is sure that any of those conditions exist,'' he said. Professional knowledge about the humpback is based on observations of healthy whales at sea, and this is the first time such a large one has gotten inland so far and so long, said Slawson.

''We've had experts give the opinion that it would be six days before it develops problems, and others say it could be six months,'' he said.