When Arlington officials met yesterday with Virginia Highway Commissioner Harold King over construction of Interstate 66 they expected King's position-like that of his predecessors-would be set in concrete.

An hour later, after King readily approved or agreed to consider a list of landscaping features for the controlversial highway, his critics were disarmed.

"This road," King assured the group at one point, "is going to be prettier than the George Washington Highway."

King, who took over the Virginia Highway Department's top job last summer, recently surprised Arlington officials by his decision to cease planning for another interstate route across the county. That project, called I-595, would have connected National Airport with Shirley Highway, and had been pressed strongly by his predecessors who favored more highway building in Northern Virginia.

King's agreement yesterday to landscaping proposals along the final 1.8 mile segment of I-66 near the Potomac River again surprised the Arlington officials. "In the past we've been told that an interstate is an interstate and that these things were out," said Arlington Board Chairman Dorothy T. Grotos. "I feel as though Mr. King agreed to 99 percent of what we asked for," she said.

King told Grotos and members of a county-appointed committee monitoring construction of the road that he was committed to making the limited-access "blend into the surrounding area as much as possible."

Lincoln McCurdy, chairman of the citizen's group said his committee had spent many hours haggling over landscaping features that it believed would make the highway look more like the GW Parkway than Shirley Highway.

After King agreed to plant "goodsized trees" along the roadway and promised to decide this week on a request for "aesthetically designed bridges" rather than standard concrete ones, McCurdy's group appeared pleased.

Members of CONTACT, an anti-I-66 group that has filed suit in federal court in Alexandria claiming that the road is being built improperly were not invited to yesterday's meeting. A county official said CONTACT members were not invited because officials feared the group would be "too disruptive."