The development that has changed Arlington's skyline, giving it new office and residential high-rises, has been a major factor in the nearly 300 percent increase in the county's real property tax base in the last nine years.

Thomas Rice, Arlington's new assessor, said the county's real estate tax base has jumped from $3.4 billion in 1977, when the county first began assessing property at 100 percent of its estimated value, to $10.3 billion today.

At the same time, Rice said, assessments on regular commercial and industrial properties have risen from 23 percent of the total property tax base in 1977 to 38 percent in 1986, the Washington metropolitan area's second-highest level. Only the District exceeds Arlington, with 44 percent of its tax base composed of commercial and industrial properties.

"It's quite evident" that the explosion in commercial development in recent years has helped ease the tax burden on residents, Rice said. But he noted that when payments by homeowners and tenants are combined, "Residents still carry the largest share of the tax burden as a single class of property." Together they make up $5.5 billion of the $10.3 billion tax base.

Single-family residential properties have jumped in value while simultaneously dropping from 53 percent of the tax base in 1977 to just over 40 percent today. Such properties today account for $4.1 billion of the tax base, more than double their $1.9 billion value in 1977, Rice said.

At the same time, commercial properties have skyrocketed in assessed value from $805 million in 1977 to $5.3 billion this year. But the latter figure includes $1.4 billion in rental apartment building properties -- 13 percent of the tax base -- that Arlington counts as commercial land.

When conventional commercial and rental properties are added together, they amount to 51 percent of the county's $10.3 billion tax base this year.

"The value of commercial property has increased 500 percent since 1977, while residential property increased by just over 200 percent, some of it from normal attrition," Rice said. "And a number of residential properties have been removed from the residential category to commercial with the consolidations" that have taken place in neighborhoods near Metro-stop development areas.

The economic boost to the county from the Metro system can be seen in assessment statistics for Crystal City and the stops along the Rosslyn-Ballston high-rise corridor.

Countywide, the average commercial property jumped 18 percent in value; hotels, however, got a whopping average increase of 30 percent. In Crystal City, the value of conventional commercial properties rose almost 28 percent from last year while the value of condominiums leaped 64.5 percent.

The latter jump is largely attributable to a reclassification of a 50-acre tract of former railroad property. With the development on the tract of Crystal Park condominiums by the Charles E. Smith Co., the assessed value has jumped from $40 million a few years ago to $168 million today, Rice said.

In the Courthouse area, condominium assessments have jumped more than 46 percent from last year. In Ballston, where construction cranes seem to pop up in new places every week, apartment assessments have increased more than 38 percent and commercial property assessments by almost 37 percent over last year.

Throughout the county, single-family homes have increased in assessed value by an average of 3.9 percent over last year, and condominiums by 3.25 percent.

Rental apartment buildings, however, have experienced sharper increases. The average garden apartment building's value jumped 20.5 percent over last year. Buildings with five or more stories increased an average of 10.5 percent.

"There's a real concern that apartment [building] owners' increased assessments could push up rents to the point where it could displace some tenants," said Rice.

Each time there is a rent increase, he said, it generally results in higher assessments because when the county assesses, it takes into consideration the owners' income from the complex as well as recent sales.

But documents prepared by Rice's office show that the rents need not correspond to increased assessments.

For example, the average garden apartment unit in a complex with eight or more units is assessed at $33,057, which would call for monthly tax payment of $25.89 per unit -- or $5.16 more than last year's monthly payment.

The County Board last month cut the 1986 real estate tax rate by 1 cent, to 94 cents per $100 assessed value. Members have indicated they plan to cut other taxes April 26 when they adopt the fiscal 1987 budget.

High on the list of priorities for cuts will be business license taxes, which County Manager Larry J. Brown has characterized as perhaps more onerous than the real estate tax on businesses.