It was 10:48 a.m. when Andrew P. Miller rapped gently on the aluminum screen door of Lizzie Turner's aging concrete block house on U.S. Rte. 340 here.

"We have some trees here and we would like to plant one in your yard," said Miller, who is seeking Virginia's Democratic nomination for governor. He told Mrs. Turner that she could take her pick of an autumn olive, ash, or sweet gum.

The 89-year-old widow picked the olive tree and moments later Miller, the former Virginia attorney general, had shed his pin-striped gray suit coat and was digging a hole in her front yard.

With only one week of campaigning before he faces former Lt. Gov. Henry E. Howell in the Democratic gubernatorial primary, planting trees was how Princeton-educated Miller spent most of today. First he planted six-inch-high seedlings around this Shenandoah Valley town, then he literally held an underground meetings with some of his supporters in Luray Cavens and later promised state aid to help restore one of the state's seven remaining covered bridges, which was destroyed by arson last year.

It wasn't until the early evening, at a meeting of Harrisonburg supporters, that Miller made his first attack against Howell.

Without naming Howell directly, Miller charged that Howell's use of more than a dozen local fund-raising committees "is a violation of the letter of the law.

"And yet our state board (of elections) apparently feels no action is necessary even though a candidate's filings do not conform to the law," Miller said.

Under the current practice, elections board secretary Joan Mahan had said that the board is powerless to take any action against the candidates who fail to comply with the state law. Any enforcement of the law is up to local commonwealth's attorneys around the state, she has said.

Miller had channeled all of his funds through a single statewide committee, a step his staff has said is required by 1975 amendments to Virginia election laws. But Howell has continued to raise funds both through a state committee and a number of regional committees, much as he did in 1973 when he ran for governor as an independent.

Miller's day in the upper Shenandoah Valley, long considered one of the most conservative regions of the state, brought signs confirming the prediction of state Del. Alson H. Smith, a Winchester Democrat who told reporters. "This is Miller country."

In fact Smith, a Miller fund raiser said that "if Howell has an organization here, it hasn't surfaced yet."

In nearby Clarke County, where Miller supporters have planted about 2,000 "Miller trees" since the start of the primary campaign, one of those joining Miller at White Post was Thomas Byrd, youngest son of conservative independent U.S. Sen. Harry F. Byrd Jr. and general manager of the Byrd-owned Winchester Evening Star newspaper.

Later, riding in a golden van to Luray Caverns, Miller expressed disappointment that President Carter's eldest son Jack has come into the state to campaign for Howell. "But if anything, it's going to be counter-productive" for Howell, Miller said.

"Selecting a governor is one thing Virginians like to preserve for themselves," Miller said. But he stopped short of saying that the younger Carter's role violated a promise President Carter made to him not to become involved in the primary. "In light of the commitment, it's unfortunate," Miller said.

Howell sought today to counter recent evidence of Miller's inroads into his black support around Virginia by releasing a list of 119 black ministers, 24 black elected officials and 14 black political organizations supporting Howell.

"Henry Howell has walked the road of human and civil rights in Virginia like no other statesman," said the Rev. I. Joseph Williams of Norfolk news conference this morning. "It is our feeling that the overwhelming majority of black ministers and black people will not forget Henry Howell."

Howell also received a $5,000 check from the Retail Clerks International Association to bolster the sagging finances of his campaign. He said the money would be used to help repay part of the $20,000 personal loan he secured today for his last-minute television appeal to Virginia voters.