When the House of Delegates took time out for lunch during last Saturday's marathon 10-hour session, one lawmaker remained in his seat while the others scurried for the snack bar.

Del. John. H. Rust Jr., a Republican who represents Northern Fairfax County Fairfax City and Falls Church, spent most of the hour-long recess poring over the more than 50 bills to be considered that afternoon.

"I just think it's important to understand what it is I'm voting on," said Rust, 32, the former Fairfax City attorney.

That kind of devotion to duty and attention to detail has won the freshman legislator widespread respect on both sides of the political aisle. Some colleagues even go so far as to say Rust is the best of the legislative newcomers.

"Business-like, serious, friendly, smart," says Del. Dorothy S. McDiarmid (D-Fairfax), one of Rust's opponents last fall for the five Northern Virginia seats from the 18th District. "He's got good antenna, and when he opens his mouth he knows what he's talking about."

Rust says he is pleased but not overly surprised by what he has discovered in Richmond. "I've found out that even if you're a freshman and a Republican, if you do your homework you can have an impact here," he says.

For a while, it appeared that Jack Rust might get lost in the pack. He came to Richmond as one of six Northern Virginia freshman, four of whom are Fairfax Republicans.

But Rust's background as a city attorney, and the fact that his grandfather served eight years in the state Senate in the 1930s as a Harry F. Byrdstyle conservative Democrat, assured him of some extra consideration.

When House Speaker A. L. Philpott doled out committee assignments, Rust got a plum -- the Counties, Cities and Towns Committee.

His fellow lawmakers say Rust has proven to be an able committee member because of his municipal law background. "He finds important problems in bills that no else would have noticed," says fellow Fairfax Republican Warren E. Barry.

But Rust's past job as city attorney also has led to some criticism.

For example, last week on a bill sponsored by Del. Warren G. Stambaugh (D-Arlington) to pay for Metro with a 4 percent Northern Virginia gasoline sales tax, Rust called Metro "a runaway locomotive," and tried to tack on an amendment that would funnel the revenue from the tax first to localities, which would then decide how much would to give Metro -- a position identical to that of the Fairfax City Council.

"Jack still thinks he's the Fairfax City attorney," fumed a another Fairfax Republican. Others feel Rust may have a conflict of interest because he still collects fees for legal work he is completing for Fairfax City.

Rust denies there is any conflict, noting that his amendment was supported by the Fairfax County Board of Supervisors as well as the Fairfax City Council. He warns that without some brakes on the Metro money, Fairfax City may feel forced to reject the sales tax, which must be approved by all Northern Virginia jurisdictions. A similar proposal was defeated there four years ago.

"It makes no sense to pass a tax that the local governments may kill," he says.

Although his amendment was killed 65 to 28, Rust split ranks with four other Fairfax Republicans -- John S. Buckley, Robert E. Harris, Lawrence D. Pratt and Barry -- and voted for the Stambaugh bill.

"You may lose battles, but you don't want to lose the war," Rust says. I have never disagreed with the necessity for the tax, though I'd much prefer Gov. (John N.) Dalton's statewide approach.