The Reagan administration's plan to deregulate natural gas narrowly survived its initial test in the Senate Energy and Natural Resources Committee yesterday, but supporters conceded that it was obvious that Congress will not buy the key provision removing price controls from all low-cost "old gas" by Jan. 1, 1986.

A "sense of the committee" motion offered by Sen. Howard M. Metzenbaum (D-Ohio), which would have put the 20-member panel on record as favoring continuation of controls that hold down the price of gas discovered before 1977, was defeated by 10 to 8, with two Democrats voting "present."

But one member who abstained, Sen. John Melcher (D-Mont.), indicated that he was doing so because he viewed the non-binding resolution as meaningless. Immediately after the poll, Sens. Henry M. Jackson (D-Wash.) and Wendell H. Ford (D-Ky.) offered an amendment setting up the first real vote on the issue next Tuesday.

"It is obvious that the bill the way it is written will not pass," Chairman James A. McClure (R-Idaho) said yesterday. "That vote indicated some movement off that provision is going to be necessary."

McClure said his panel will spend next week considering possible compromises such as phasing out controls over a period longer than the two-years envisaged by the administration.

"If Metzenbaum had won today and killed decontrol of old gas, that would have been more significant than Metzenbaum having lost," Sen. J. Bennett Johnston (D-La.), a supporter of decontrol, agreed. "But to decontrol old gas will take a number of different votes. This bill has got a long way to go."

Nevertheless, the Reagan administration--which had worked hard in preparing for the first test on its proposal--took modest satisfaction in winning.

"This vote allows us to continue moving ahead with this bill," said Robert C. Odle Jr., assistant secretary of energy for congressional relations. "There are going to be setbacks and negative votes sooner or later, but so far every major issue seems to break our way."

Sen. John Heinz (R-Pa.), who with Sen. Mark O. Hatfield (R-Ore.) broke ranks with the Reagan administration, noted before yesterday's poll that the committee and the Congress are "clearly narrowly split" on the controversy.

Opponents of decontrol of old gas contend that it would result in a windfall of more than $40 billion for the major oil companies, and Metzenbaum yesterday argued that it would "cost every household an average of $1,000 over the next three years in increased" heating bills.

"It is my belief that we are kidding ourselves if we think basically that a decontrol of old gas bill can get through the Congress," Heinz said. "I think if we report a bill that has decontrol of old gas, we are whistling in the dark. I don't think anything is going to happen."