Virginia Gov. Charles S. Robb last night rejected a legislative proposal that would determine defendants' eligibility for free legal counsel in criminal cases solely on the basis of the defendants' income.

The governor, wrapping up his review of the 1983 General Assembly's work, said the new standards for indigent defendants could prove unconstitutional. In their place he proposed a more flexible formula that would take into account a defendant's indebtedness, assets and financial obligations in determining whether he is eligible for a state-paid attorney.

"In the opinion of the attorney general," Robb said in his message to the legislators, language setting indigency standards on the basis of the U.S. poverty index "can be challenged on the grounds that it would require the trial court to deny court-appointed counsel on the basis of income alone." The criteria passed by the legislature would require a defendant with a family of four to earn less than $11,446 to qualify for free legal defense.

Robb's proposal was in the form of amendments to the state budget as he concluded his review of 647 bills passed by the legislature, rushing to meet a midnight deadline. In all, Robb signed 538 bills, vetoed 25, of which 22 were duplicates of other measures, and suggested amendments to another 39.

The General Assembly convenes April 6 to vote on the Robb proposals. Little of what the governor did yesterday is expected to cause controversy.

The proposal to limit access to state-paid counsel for poor criminal defendants received little notice during the legislature's six-week session, but in the last weeks the standards came under attack from lawyers and experts who said they would hamstring judges and set an arbitrary limit on what has been established by the U.S. Supreme Court as a constitutional right to legal defense against criminal charges.

Even some legislators were unaware of the language included in the budget, which had been negotiated during the final days of the session by a six-member conference committee meeting privately.

The proposed criteria originated in the Senate, where Finance Committee members had offered it as a means of keeping the lid on the rising cost of providing free defense counsel in Virginia.

Those increases--from $4.3 million in 1979 to $8.3 million in 1982--reflect a problem shared by other states. But according to experts, no other state has attempted to resolve the issue by slapping an income limit on defendants.

The language that emerged from the legislature " was capricious and inartfully drawn," said Matthew Ott, a Richmond criminal defense lawyer and a member of the Virginia State Bar's criminal law section, adding: "And since it was presented at the 11th hour, it allowed no input from people, pro or con."

Among the bills Robb vetoed was one sponsored by Del. Alan Diamonstein (D-Newport News), state Democratic Party chairman and a close friend of the governor's, that would have allowed certain narrowly defined roadways to be considered a state responsibility. The bill had been introduced at the behest of a former legislative colleague of Diamonstein's who owns property that would have benefited from its passage. In his statement to the legislature yesterday, Robb said the Diamonstein bill "had not been fully understood."