Air travelers between New York and the West Coast will continue to get a price break through the summer despite a modest increase in the fares effective July 1.

Over the weekend, Eastern Airlines announced that it will raise its one-way regular coach fare on July 1 from the current $99 to $129 and hold it there through Aug. 1. Trans World, American and United Airlines all matched the price yesterday. A one-way coach fare from Washington to California on the major airlines costs $284.

World Airways said yesterday it would peg its unrestricted one-way fare between New York and West Coast cities at $110 from July 1 through Sept. 7. "We will not be undersold," Edward J. Daly, World's president and chairman, said yesterday, again. World had dropped its one-way fare of $140 to $88 last month to meet Eastern's $99 initiative.

World will continue its $140 price for flights between Baltimore/Washington International Airport and the West Coast but will offer the $110 fare on a night flight from Los Angeles to BWI.

The transcontinental air fare war broke out last month when Eastern Airlines entered the market and began offering the $99 fare to try to attract customers. The other major carriers soon met Eastern's fare, though they complained that none of them would make money at that fare. They had hoped the fares would rise after Eastern's June promotion ended. Two weeks ago, TWA announced it would raise its one-way fare to $250 on July 1 in an attempt to bring coach fares to a "more realistic" level even though it said it would continue to offer discount Super Saver fares for round-trip tickets bought a week ahead of $298 for day flights and $268 for night flights. But it acknowledged at the time that it probably would not stick to the $250 proposal unless other airlines followed along.

In other fare news yesterday, United announced the resumption of its family plan for travel in the continental United States. Effective today through Dec. 15, under the plan the first adult will pay full coach fare; the spouse, 50 percent; and children under 18 years of age, 40 percent. If only one parent flies, the first child pays 50 percent, and additional children fly at a 60 percent discount.

United also cut the fare between Denver and San Francisco to $80 each way from a normal fare of $170 beginning Saturday.