Canada is expected to increase by a stiff 20 percent the price of its natural gas exports to the United States, a price rise that would add $500 million to consumer bills the first year it is in effect, according to senior Carter administration officials.

The Ottowa government is likely to make its announcement, raising the cost of natural gas from $2.30 to $2.80 per thousand cubic feet, after a Cabinet meeting Prime Minister Joe Clark called for today.

Canadian officials say the increase the second in recent months, is justified by ths sharp increase in world oil prices imposed by the Organization of Petroleum Exporting Countries.

Last month the seven-member National Energy Board recommended that Canada, which supplies 5 per cent of U.S. domestic gas consumption, raise its prices sharply.

Yesterday a Canadian official declined to speculate whether the announcement of the price increases would be made today or later in the month, but added, "I don't see any possibility the number will be too different from $2.80."

Senior Energy Department officials say the expected gas price increase would have a major impact on parts of the United States highly dependent on Canadian imports, including: the Pacific Northwest, Minnesota, Wisconsin, North Dakota and Montana.