The Arlington County Board voted yesterday to place a $13 million bond referendum for Metrorail construction on the November ballot, rejecting an earlier plan to ask voters to approve a $40 million bond that would help cover much of the county's current financial obligation to the 101-mile subway system.

The decision to place a $13 million Metrorail bond referendum on the ballot means that the board will have to put a similar measure before voters next year and possibly beyond if the county is to continue to pay its share toward the completion of the system, which receives federal, state and local funding. The $13 million bond will raise only enough money to cover the county's financial obligations to the system through next year, county staff members said yesterday.

Metro officials now compute Arlington's financial obligation to the system to be $64.3 million.

The board also voted to place three other bond referenda totaling $8.1 million on the ballot to pay for street, highway and community conservation projects and improvements to the county's water distribution system.

The board rejected a $1 million bond referendum proposal to fund park and recreation projects but agreed to consider taking $500,000 from general funds to finance them.

An Arlington citizens committee on Metrorail financing, headed by former County Board chairmen Joseph S. Wholey and Stephen H. Detwiler, had proposed that the county raise $40 million toward meeting that obligation through the fall referendum and raise the remainder from "pay-as-you-go" capital and state aid.

But board members, wary of the defeat in 1975 of a $25 million bond referendum for Metrorail construction, unanimously approved the lower figure.

Board Vice Chairman John Milliken said the 1975 Metrorail bond referendum was defeated largely because voters were unsure how the money would be spent.

Milliken said there were still too many unanswered questions about how the $40 million in Arlington funds would be spent on the system if raised this year and whether the figure is appropriate because state and federal funding for Arlington's share of the project is subject to change.

Board member Dorothy T. Grotos, who reminded the board of the 1975 bond referendum defeat in making the motion for the $13 million bond referendum, said, "There are so many unknowns in dealing with Metro, I am uncomfortable in going to the public" with the $40 million bond proposal.

In explaining the board's action, Milliken said after the meeting, "I think all of us on the board want this bond issue to pass."

Milliken unsuccessfully tried to place a $22.7 million Metrorail construction bond proposal on the upcoming ballot. His plan was also defeated to have a bond referendum of a similar amount in 1986.

Yesterday's vote on the Metrorail bond proposal also reflects a decision made by the board a few years ago to put such major referenda on the ballot only in even years, when national elections increase voter turnout.

In yesterday's action, the board did not indicate the amount of the proposed Metrorail bond likely to be presented to voters next year.

Board Chairman Ellen M. Bozman, who favored placing a larger bond before the voters, reluctantly went along with the vote after saying she felt uneasy raising "the bare, bare minimum." She said doing so may not be financially prudent.

Board member Walter L. Frankland said he fears that placing a $40 million bond referendum before voters would jeopardize passage of a Metrorail bond this year as well as bonds for county improvements.