The Civil Aeronautics Board yesterday took steps to authorize new air service between the East and West coasts at one-way fares as low as $99 without restrictions.

The lowest current unrestricted roundtrip coach fare from here to California is $414, with an increase in the offing. The lowest scheduled fare now available to California is $207 round-trip - but only for passengers who fly during the middle of the week after 9 p.m., buy their tickets 30 days in advance, and stay away between seven and 45 days.

At its meeting yesterday, members of the board instructed the staff to draw up a formal order that would:

Add at least three new airlines to four popular cross-country routes - from Washington and New York on the East Coast to Los Angeles and San Francisco on the West Coast - to complete with the existing big three.

Give two charter airlines the authority to operate domestic scheduled services for the first time. One of theim is World Airways, which has been seeking CAB approval to offer lowfare schedule transcontinental service for more than 10 years.World Airways plans to offer the $99 oneway fare.

Give Pan American World Airways its first mainland domestic routes.

Tbe board's tentative decision in theis case draws together many of the pro-competition, marketplace-oriented threads that have appeared in other recent decisions.

Instead of its usual practice of dolling out a route to a single carrier, the board has epted to grant new route authority to a number of airlines, to be used or not used as they determine. The agency also decided to place no restriction or conditions on the new authority, allowing the airlines to decide which airports they're to use, what fares to charge and how often to fly. The board's decision also would remove to one-stop requirement on American Airline's current authority to fly to San Francisco from here.

World Airways originally asked the CAB for permission to fly cross-country from airports generally considered under-utilized. It proposed going from Newark and Baltimore/Washington on the East Coast to Oakland and Ontario in California. At yesterday's meeting the CAB members appeared to be unanimous that the airlines should be able to fly from and to any airport they select.

Besides its impact on the price of transcontiental air travel, the board's decision - expected to be final by Thanksgiving - could also affect the entire domestic price structure CAB officials believe the decision could bring even more travelers to the air - 4 million currently fly cross-country each year. It may also have a significant impact on the three major airlines - American, United and Trans World - facing new competition; the cross-country routes are the heart of the domestic route systems of all three.

Besides World, Capitol International Airways was also selected tentatively for the new routes. Pan Am's first domestic route will be between New York and California; it did not ask for authority to fly to and from the Washington area. Pan Am told the CAB that it would offer a general coach fare 25 percent below the current coach price - approximately $300 - and would have a standby fare of 50 percent off.

At its meeting yesterday, board members decided to discuss later whether go give World Airways a head start of six months or a year on its new routes before letting in the other airlines, but the discussion indicated such a plan would not get a board majority. World Airways is seeking a three-year head start.

"In a way, they deserve it," Chairman Alfred E. Kahn said, in outlining the low-fare proposal. "They've been around 10 years with this innovative proposal."

On the other hand, he said, the board has favored competition and stimulating the marketplace as much as possible to give airline managements more decision-making power. The cross-country routes would offer the "clearest possible test of the efficacy of competition," he said.

World Airways filed its original application with the CAB in 1967 asking permission to institute scheduled cross-country air service at a $75 fare; after sitting around for five years, the application was then dismissed as "stale."

It refiled its application - with a slightly higher fare proposal - later and was told by the CAB that the law didn't permit the issuance of scheduled authority to a charter airline. World sued and won an appeals court order that the CAB could legally consider the application.

The board's actions in the World Airways matter became one of the examples used by proponents of deregulation to show that the practices, procedures and policies of the board needed updating.