By a surprisingly wide 84-to-10 margin, the House of Delegates voted today to broaden the state's Freedom of Information Act and open the doors to some crucial but traditionally closed legislative meetings.

The bill now goes to the Senate, where its chances of passage have been enhanced by the decisive House vote, supporters said.

The legislation would, among other things, require the sometimes secretive House Appropriations Committee and the Senate Finance Committee, which handle state spending bills, to open all their meetings.

Excluded from the open-meeting bills are meetings of judicial selection committees of the General Assembly and other groups dealing with personnel, the Joint Legislative Audit Commission and the State Government Management Commission. The latter two groups would be permitted to hold closed sessions to protect the confidentiality of their sources, according to Del. James H. Dillard II (R-Fairfax), sponsor of the House-passed bill.

Both committes traditionally have met in secret when deciding what changes to make in the governor's proposed budget. So secretive has been the Senate Finance Committee that last year it refused even to admit a fellow senator who was not a member Wiley F. Mitchell Jr. (R-Alexandria).

Excluded from the open-meeting bill are meetings of judicial selection committees of the General Assembly and other groups dealing with personnel the Joint Legislative Audit Commission and the State Government Management Commission. The latter two groups would be permitted to hold closed sessions to protect the confidentiality of their sources, according to Del. James H. Dillard II (R-Fairfax), sponsor of the House-passed bill.

Hours after the House action today the Senate Finance Committee was scheduled to hold one of its secret meetings - on budget changes for the biennium ending June 30, 1978. The group's budget subcommittee which includes senior senate members is sometimes called the "secret seven."

It its last action before the deadline for passage of bills introduced by its members, the House approved five bills proposing $200 million in general obligation on bond issues to finance construction at state colleges, prisons parks and the port of Hampton Roads.

All five bond bills passed by a wide margin although several delegates denounced what they described as a hasty assembling of projects to meet the deadline for House action. Del. James M. Thomson (D-Alexandria), said the projects were approved by an Appropriations Subcommittee, but members of the subcommittee said it never met.

Almost all of the projects, however, have been on Godwin administration lists of needed facilities for several years.

The bond issue bills now go to the Senate, where they are expected to be reduced in size. Any board proposal finally approved by the Assembly will be summitted to voters in the Nov. 8 general election.

The proposals approved today include about $52 million in construction at Northern Virginia Community College, George Mason University, Mary Washington College and two other universities with high ratios of Northern Virginia students - the University of Virginia and Virginia Polytechnic Institute and State University.

While 33 other states have laws prohibiting legislative secrecy, Dillard said he decided to engage in extensive one-on-one lobbying to win votes - both during the first major test, in committee, and later on the House floor.

Joining Dillard as sponsors were delegates ranging across the political spectrum, from liberals like Del. Warren G. Stambaugh (D-Arlington) to conservatives like Del. Robert B. Ball Sr. (D-Henrico), as well as three of the 20 members of the House Appropriations Committee.

Backing up the Dillard group's efforts was Common Cause of Virginia, which prepared a questionnaire asking the delegates how they stood on a broadened Freedom of Information Act. In replies early in the session, 40 of the 100 delegates indicated they would support such legislation, 10 said they would oppose and 50 did not answer.

The Dillard group apparently was able to prevent any negative votes among the 50 who didn't reply to the questionnaire.

Judy Goldberg, chief lobbyist for Virginia Common Cause, said the wide support for the bill - which surprised both her and Dillard - might have been partly due to the election-year atmosphere. "It's a hard thing to oppose opening up sessions when it could become material in a campaign," she said. All 100 House members face re-election campaigns this year.

Besides prohibiting secret meetings by most General Assembly committees, the Dillard bill would open up most legislative study commissions, all gubernatorial study groups and study commissions appointed by local governing bodies.

In a busy day, the House acted on a number of measures, only a few of them controversial. The delegates:

Approved, 72 to 23, a bill that would permit dismissed public school teachers to put their case before an impartial fact-finding committee. The findings would go to the school board in the district where the teacher was employed. The school board, whatever the findings, would retain ultimate authority to uphold or rescind the dismissal.

Narrowly passed, 49 to 47, a measure creating a Local Government Cooperation Assistance Act that would provide state money and technical expertise for neighboring localities that wants to explore joint projects, such as construction of a sewage treatment plant. The close vote indicated the growing disenchantment with state planning efforts on the local level.

Approved, 70 to 23, a bill that is aimed at encouraging physicians to prescribe cheaper generic drugs, rather than brand name drugs.

Voted 57 to 28 to approve a bill to permit "instant bingo" using prepunched cards. The games could be sponsored by those charitable groups that now are permitted to conduct regular bingo. The bill is expected to face trouble in the Senate.

Approved, 97 to 0, a bill tightening requirements on reimbursements to General Assembly members and state employees for expenses they incure while conducting official business. The bill was in response to news reports detailing how some legislators used telephone credit cards to make personal calls.