State budget cuts, manufacturing delays and unexpectedly high construction bids have thrown into doubt the planned October start of Northern Virginia's commuter rail service and could mean fewer trains on the line, rail officials said.

Virginia Railway Express managers must contend with a 10 percent cut in their first operating budget because of an $800,000 reduction in state funding. Construction bids for 11 of the system's 17 station platforms recently came in nearly twice as high as railway officials expected. In addition, the railway car manufacturer is having trouble getting enough steel to finish the 28 new cars scheduled for delivery this fall.

However, rail officials say they can still open on time. They say they will reopen bids on platform construction, and could purchase used cars from Boston and dip into their emergency reserve fund to solve other problems.

"Every delay makes it a little bit tougher. We don't have much of a cushion," said Prince William Supervisor Edwin C. King (D-Dumfries), a member of the railway's operations board. "I do think we'll start."

The railway, which is to use two existing rail lines to carry an estimated 4,500 commuters a day between the District and as far away as Fredricksburg, has had an on-again off-again history since it was proposed more than a decade ago.

For railway officials, the budget shortfall poses the biggest problem, because they must find an alternative source of funds or run fewer trains than the planned eight daily round trips -- four between D.C. and Fredericksburg and four between the District and Manassas.

The railway had expected to receive $2.8 million from the Virginia Department of Transportation as the state's contribution to its $8.6 million first-year operating budget. But the department's assistant administrator, Charles Badger, said the railway probably will get only $2 million, because Gov. L. Douglas Wilder (D) has recommended a $4 million cut in the state's mass transit budget.

Railway Manager Thomas R. Waldron has proposed borrowing $800,000 from the railway's $2.4 million emergency capital fund, and then repaying it when ridership increases and revenue improves.

"We shouldn't have any trouble replenishing it in the second year," Waldron said, adding, "I think this qualifies" as the type of emergency the fund is supposed to be used for.

Badger called the borrowing plan "unusual," and said, "We don't like to see them mortgage their future unnecessarily."

Railway officials say they are loath to increase fares because marketing surveys show that commuters already think the planned fares are high. Monthly passes for commuters traveling between the District and Fredericksburg would cost $184, or $8.33 daily, and those traveling between Woodbridge and the District would pay $140 a month, or $6.37 daily.

Railway officials said they had expected depressed conditions in the construction industry to help keep platform bids down. But only two companies bid, rather than the expected 20.

Rather than ask one firm to build all 11 platforms, railway officials may seek separate contracts for each line, King said.

Fairfax Supervisor Sharon Bulova (D-Annandale), who heads the operations board, said she believes the new bids will set construction behind by only a month. Still, rail planners have expressed concern about cost overruns, because they haven't yet received bids on rail storage yards in Spotsylvania County and Manassas, and a platform at the District's L'Enfant Plaza.

Rail officials are negotiating to buy and renovate 25 used cars from Boston, for use if the new cars do not arrive on time. Any such deal, however, would need approval from the coalition of sponsoring local governments.

In addition, one of the 17 planned stations, at Lorton, already has fallen behind schedule, and railway officials said they are concerned that Stafford County officials still haven't found a site for the Brooke station.