Gas company officials warned yesterday that President Reagan's plan to deregulate natural gas would, in the words of one, be "pure disaster" for their already angry customers.

The officials testified as the Senate Energy and Natural Resources Committee ended four days of hearings on the controversial administration proposal to remove all controls on natural gas by 1986, a plan Reagan says will cut prices and end complaints of consumers hit by price increases of 40 to 50 percent a year.

All said they favor eventual decontrol but that they do not want it now or as proposed by Reagan.

C.M. Butler III, chairman of the Federal Energy Regulatory Commission, said the administration bill needs some changes but urged Congress not to delay action "while it searches for an easy and painless solution.

"No such solution exists," he said.

Committee Chairman James A. McClure (R-Idaho) said any legislation would have "to achieve a balance between the need to limit consumer gas prices and the equally important need to ensure that gas shortages do not occur later in this decade."

John Abram, chairman of the Southern California Gas Co., said his firm's 13 million customers are "justifiably upset and angry" about "skyrocketing" gas rates. "Many low-income people are finding it hard or impossible to pay winter gas bills," he said.

Reagan's plan would not correct that situation, Abram said, but would "create chaos and confusion" within the industry while increasing profits for producers. "It would be pure disaster for the residential gas consumers of America," he said.

Columbia System Gas President John Croom said the administration plan has "basic flaws," among them the proposal to lift existing price controls on "old" gas, that produced from wells drilled before 1977.

O.C. Davis, president of the MidCon Corp. of Chicago, said, "we vigorously oppose" the plan to lift controls on "old" gas at the end of 1985, saying it would "cause chaos in the natural gas markets and would result in higher prices to the consumer."