For more than a year, hardly an issue has come before the Arlington County Board without board member John G. Milliken sizing it up on what he calls his "livability index."

"What we have to look at is: Is Arlington the kind of community you want to walk through on a Sunday morning or a Tuesday evening?" he is fond of saying.

It has been an incessant topic for Milliken, the Democratic lawyer who stepped down yesterday as board chairman, and for the board's four other members.

"We're not at a perfect 10, but we've made real progress," Milliken said recently as he discussed his year as head of the county's governing body.

County Board members say the livability index is the product of a myriad of minor and major decisions they think will make Arlington a better place to live and work in -- issues ranging from the removal of unsightly weeds to an overhaul of the county's road network and an expansion of its supply of affordable housing.

"These are issues the community is going to be wrestling with for probably the next 10 years," said Milliken, who was reelected to a four-year term in 1984.

While he was eager to talk about long-range goals for Arlington, Milliken, 40, was not ready to say whether he had decided to seek the Democratic nomination to challenge Rep. Frank R. Wolf (R-Va.) this fall.

"I don't make any secrets about having thought about it," said Milliken. "I will continue to think about it and I suspect I will have more to say" early this year.

An aide to former Democratic representative Joseph L. Fisher of Arlington and a member of the same Washington law firm as Walter Mondale, Milliken has been increasingly active in Virginia Democratic politics.

A native of Loudoun County, he lacks a base in Fairfax County, the most populous jurisdiction in Wolf's 10th Congressional District.

But 1986, Milliken notes, is the a year in which there are no major local elections in either Fairfax or Loudoun to draw out the counties' normally Republican vote.

And Arlington, which has a stronger Democratic vote, is likely to have a spirited race for prosecutor, which could help a Democrat, Milliken says.

For now, however, he said, he wants to concentrate on ways of improving Arlington's future as the county's unprecedented pace of development and revitalization continues. Besides changing the Washington skyline, development has also brought the county a stronger tax base and a wider assortment of urban problems, he said.

"We can make and keep Arlington a very livable community, but only if we take the benefits of development and plow them back into the community itself in the form of parks, recreation, a sprucing up, and improvements to older retail areas so they don't suffer from neglect," Milliken said.

The county's increased tax revenues, he said, could be used for some improved programs, particularly if the county's federal aid is cut as the Gramm-Rudman-Hollings measure threatens. Many other new projects and programs should be financed either by the private sector or in cooperation with the county, Milliken said.

"I don't see why, by the time development has run its course, we can't also have completed all the things we want to do to make this the attractive, sparkling community we want it to be," he said.

Milliken outlined areas where specific improvements could be made to increase the county's "livability:"

*Transportation. The board is scheduled to adopt a revised master transportation plan early this year that will call for improvements to the roads and to hiking and biking paths. After those segments of the plan are adopted, the board will begin its study of mass transit needs.

County traffic patterns are expected to change in June after the Orange Line is extended from Ballston, its current terminus, to Vienna. Milliken said the county may want to make additions or changes in bus routes to make it easier for people to travel throughout the county.

He said the county may also want to consider starting its own jitney bus service, something like the Fairfax and Alexandria bus lines, and expanding the experimental cut-rate subway-shuttle taxicab services, particularly in the developing high-rise corridors. A continuing concern, he said, will be improving pedestrian access around the county's high-rise neighborhoods.

*Neighborhood Shopping. The board made headway last year in its efforts to stem the exodus of community stores, such as supermarkets, that the county was losing to high-rise redevelopment.

In the future, Milliken said, the county will want to make substantive improvements to the Columbia Pike corridor and consider a possible increase in the county's share of business conservation funds, money used to match contributions from merchants for the renovation of smaller business or shopping areas.

In the past, the county has put up matching funds that have led to dramatic changes in older shopping areas in Westover, Lee Heights, Cherrydale and elsewhere.

*Housing. Diminishing federal aid will make it more difficult for the county to expand its scarce supply of low- and moderate-cost housing. Last year, the county was able to help preserve some residential complexes, such as the Westover Apartments, as rental housing because of the availability of federal subsidies.

But with anticipated losses in federal money for rent subsidies and community development grants, Milliken said, the county may want to prod the state government to fill part of the gap.

*Esthetics. Milliken said he would like the county to set a goal for the eventual elimination of all "problem properties" in business and residential neighborhoods, and of all overhead utility lines. The county has authority to require underground lines in some new developments, but needs to consider what should be done in the rest of the county, he said.

The county should also consider taking over maintenance of many state roads in Arlington, if the state will give the county the funds it would have spent, Milliken said. Citing overgrown median strips and other problems with state-maintained roads, he said the county could do a better job with improving the appearance of its streets.

He said that school grounds, which he described as the "stepchild" of county maintenance efforts, need "significant" improvements and should be a priority.