The long-awaited opening of Interstate Rte. 66 inside the Capital Beltway will probably be delayed from this fall until early 1983 because of last winter's bitter cold and other factors, highways officials said yesterday.

The projected delay may be necessary to insure that the controversial highway's safety features, such as lighting and traffic control, are operational, according to Donald E. Keith, Northern Virginia director of the state's Department of Highways and Transportation.

Highway officials also said the cost of the 9.6 mile limited-access highway between the Beltway and the Roosevelt Bridge has jumped from $170 million to between $200-$275 million.

During the next two weeks, Keith said, state and local highway officials will meet to fix "once and for all" an opening date. They will also attempt to determine whether anything can be done to speed up the road's opening.

"We have to appraise the amount of delay caused by the weather," Keith said. "Whether it's the weather or whether someone just sat on their duff, that's what we're going to find out."

A state highway spokesman later confirmed that planners have recently "kicked around" an opening in January. According to Keith, construction materials -- "everything from lamp poles to crushed stone" -- have been arriving behind schedule. Another highway official blamed one month's delay on January's cold, which brought construction to a halt.

When construction began in 1977 -- after years of opposition by environmental and neighborhood groups -- part of the highway from the Beltway to Rte. 7 was expected to open to commuter traffic by 1980. The remainder was to be completed by early this year.

When it eventually opens, the highway, recently christened the Custis Memorial Parkway in honor of the Virginia family whose members included Martha Washington, is expected to save Fairfax commuters up to 15 minutes travel time to Washington.

Keith said yesterday that an announcement of the opening will be made by mid-April. "We're trying to get down to the fine line so we won't have to go through the date-adjusting bit again," he said. "We want to spend the next 8-to-9 months educating the public so that when we open I-66 there will be thousands of car pools waiting to get on."

Under a 1977 agreement between Virginia and the federal government, travel on the highway will be restricted to car pools during "peak periods" and trucks will be prohibited at all times. Keith said state highway officials are still trying to define what is meant by "peak". Answers to those questions and others will be determined in meetings during the next two weeks, he said.

According to Joseph L. Presbrey, a highway spokesman, an information program to educate commuters will begin once the opening date is fixed. "We're going to have brochures, exhibits, car pool information, TV spots, or rather public service spots . . . all predicated on when we open the highway," he said.

Keith said that without the education effort motorists might be confused by what they find when the highway opens.

"You might get a red light on an access ramp -- something you never got before," he said. "Before, you went down and took your chances as to whether or not there was going to be a traffic jam just ahead. Now we're going to have a computer at our Columbia Pike headquarters that will monitor traffic and allow cars on when traffic permits."

Keith also said acronyms like HOV will appear on parkway signs. "HOV means 'high occupancy vehicle'" -- carpool vehicles -- he said. "You'll see signs that say 'HOV this lane,' so you're going to have to know what that means."

Some commuters already are benefitting from the parkway. Recently, Metro began running buses along a small segment of the four-lane highway, cutting a few minutes travel time to the Ballston Metro stop, the last one on the Orange line in Arlington.

Extended bus service along the highway, from the Beltway to the Ballston stop, is to begin June 21, a Metro spokesman said yesterday.