Virginia highway officials sought yesterday to clear up last-minute confusion about car pool restrictions and other rules governing use of the long-controversial 10-mile section of Interstate Rte. 66 from the Capital Beltway to the Theodore Roosevelt Bridge.

The four-lane highway, officially named the Custis Memorial Parkway, will open Wednesday at 6:30 a.m., officials said. Eastbound traffic will be restricted to buses and four-member car pools on weekdays from 6:30 a.m. to 9 a.m. The same rules will apply to westbound traffic between 3:30 p.m. and 6:30 p.m. Heavy-duty trucks--those with six or more tires--will be prohibited at all times.

At a briefing yesterday, officials said several points appear to have caused confusion among motorists:

* The car pool requirements will only apply to traffic on I-66 between the Beltway and the Theodore Roosevelt Bridge. Officials said no similar restriction will be imposed on traffic west of the Beltway, as some motorists mistakenly believed. The confusion stemmed partly from signs posted outside the new highway that mention the "high occupancy vehicle," or "HOV 4" car pool requirements.

* A computerized traffic-control system, including special signal lights at entrance ramps, will not go into operation until next spring on I-66 or on Shirley Highway (I-395). The television-monitored system is intended to help keep highway traffic flowing smoothly. Officials also said they plan to take steps to prevent the ramp signals from causing traffic backups in adjoining neighborhoods.

* An exemption from the rush-hour car pool restrictions will not be granted to drivers heading to or from Dulles International Airport until next fall, when an extension connecting the Dulles Access Road with I-66 is expected to be completed. Only then will Dulles commuters be allowed to disregard the car pool requirement.

* Drivers will not be granted a grace period for compliance with car pool and other restrictions on I-66. "We intend to have a strong enforcement program," said 1st Sgt. D. W. Robertson, who is in charge of State Police patroling the I-66 section. Noting that the restrictions are spelled out on highway signs, Robertson added, "I don't see how a person can plead ignorance."

The penalty for violating the rush-hour rules will normally be a $45 traffic ticket, including a $25 fine and $20 in court costs, police said.

One still-unresolved issue is whether Washington-bound commuters on the George Washington Memorial Parkway will continue to be permitted to enter a ramp leading to the Theodore Roosevelt Bridge. Virginia highway officials hope to restrict this entrance to four-member car pools during morning rush hours. The National Park Service, which owns part of the ramp and regulates the parkway, has refused to impose the restriction.

State and federal officials said the issue is still under study, though an announcement is expected before Wednesday's opening.