The Virginia Senate today passed a bill backed by the state's powerful trucking lobby that would allow tractor-trailers as long as 60 feet on the state's roads and highways.

The bill, which the Senate approved 29 to 10, already has passed the House and now goes to Gov. Charles S. Robb. A spokesman for Robb said the governor has not yet taken a position on the bill.

Supporters say the longer trucks -- five feet longer than now allowed -- will help the state compete for business it would otherwise lose. Opponents of the measure unsuccessfully argued that the larger trucks pose a serious safety hazard on congested city streets and narrow country roads and accelerate the deterioration of state roads.

"These longer trucks should keep off the city streets and country roads where they can't operate safely," said Sen. Clive L. DuVal II (D-Fairfax), chairman of the Northern Virginia caucus.

Northern Virginia officials in recent years have blamed the use of large tractor-trailer rigs for an increasing number of truck-related accidents on local roads and for contributing to massive breakdowns of roads in congested city areas such as Rte. 1 through Crystal City. The five-foot increase in length would enable trucks to carry 10,000 more pounds of cargo.

"We'll be playing chicken on the highways," said Sen. Robert C. Scott (D-Newport News), an opponent of the bill who just hours before the Senate voted held a news conference in which he showed a graphic videotape of a large truck careening down the highways of California, clipping street signs and battering curbs.

The state is currently participating with Maryland in an experiment to ban trucks from left lanes of the Capital Beltway in an effort to reduce truck- related accidents. Maryland's law limits truck lengths to 55 feet, the same as Virginia's current law.

The bill is seen as part of a nationwide effort by trucking interests in increasingly competitive markets to open up state roads to the larger trucks. Some states, mostly in the West, allow trucks as long as 75 feet.

Under interstate commerce rules, states are not allowed to regulate the size of trucks using interstate highways and certain major access roads. The regulations imposed by the General Assembly would apply to trucks using most state roads.

The original Virginia bill, introduced by Del. V. Earl Dickinson (D-Louisa), would have allowed 65-foot trucks, which would translate into a saving of up to $100 a truckload for his lumber mill. The House, in a compromise supported by the State Highway Department, approved the 60-foot length.

In a report released in January, the Virginia Department of Highways and Transportation estimated it would cost the state as much as $9 billion to improve all of its primary and secondary roads to accommodate the larger 65-foot trucks.

Several rural state senators said the bill is needed to support Virginia's vast agricultural and manufacturing industries that could lose business to other states if the larger trucks are not allowed.

On another trucking issue, the General Assembly has approved and sent to the governor a proposal allowing any Fairfax County police officer who receives special training to order unsafe tractor-trailer rigs off the highways. Under current law, only state troopers are now allowed to detain trucks that violate safety regulations, according to Sen. Richard L. Saslaw (D-Fairfax), sponsor of the bill, which applies only to Fairfax County.