Gov. Charles S. Robb said today he has vetoed 23 bills and requested amendments to 28 others passed by the 1985 General Assembly. One of the changes Robb is seeking would allow the immediate appointment of Virginia's representative to the Washington Airports Authority.

Robb said the representative could help secure congressional approval of a proposal turning over National and Dulles airports to an interstate authority.

The governor said he worked into the night Monday to complete action on the 640 bills sent to him by the General Assembly. He signed 589 of them, most of which go into effect July 1. He said 19 of the vetoed measures were duplicates or near duplicates of legislation already signed. The assembly reconvenes April 3 to consider the amendments and vetos. A two-thirds vote of the assembly is required to override a gubernatorial veto.

Robb signed a Democrat-sponsored bill raising Virginia's beer-drinking age to 21 in two stages but withheld his signature from another, sponsored by a Republican, that would have accomplished the same objective a year sooner.

The governor will also seek amendments to a bill giving people accused of drunken driving the right to select either a blood or breath test, but not both. Robb noted that the bill could permit someone suspected of drunken driving to go free if either the blood or breath test was not available. His amendments would require that when only one test is available, it will have to be taken.

The governor said he withheld his signature from a measure introduced by Sen. Peter K. Babalas (D-Norfolk) that could have helped a defunct firm in a legal battle with Virginia Beach over the ownership of waterfront property worth $1.8 million. It would have required a court to dissolve the receivership that has overseen the firm and land for 44 years, strengthening the company's claim to the property. Lawyers for Virginia Beach said the land is now public.

Another proposed amendment calls for safeguards to a patronage bill that removes from the grievance system 508 top managers, including prison wardens, and makes them directly accountable to the governor. Robb requested antidiscrimination language and reinstatment of internal auditors in the grievance system.

The governor requested a budget amendment that forces the state Compensation Board to pay overtime to sheriff's deputies who often work extra hours without compensation, bringing the state in line with a decision by the Supreme Court on wages for state and local employes.

Robb also withheld his signature from the supplemental budget bill to insert an amendment allowing for the employment of more full-time local law enforcement officers.