Arlington attorney Elise B. Heinz took an early lead yesterday in the race for the Democratic nomination for the 23rd District floater seat, representing Alexandria and Arlington, in the Virginia House of Delegates.

With 10 of 70 precincts reporting, all of them from Alexandria, Heinz had 52 per cent of the vote to 37.2 per cent for Alexandria attorney Robert L. Montague, James McCaskill, an Arlington high school teacher, was running third with about 10 per cent of the vote.

With only one precinct reporting in the four-way race for three seats in the 22d District delegate race in Arlington, incumbent delegates Mary A. Marshall (D-Arl.) and Warren G. Stambaugh (D-Arl.) were each comfortably ahead, with 131 and 108 votes, respectively.

Marianne S. Karydes, the 43-year-old former chairman of the Manpower Planning Council held a three-vote edge over assistant Commonwealth's Attorney James F. Almand.

The real contest for the Democratic nominations was between Karydes and Almand, the two nonincumbents. Incumbents Stanbaugh and Marshall ran as a team and sent out joint campaign literature.

Karydes and Almand both had energetic campaigns. They walked through precincts, telephoned residents and appeared at just about any gathering that contained more than three registered voters. The main point separating the two was not issues - on which, for the most part, they agreed - but the question to replace John L. Melnick (D-Arlington), who left his 22d District seat to run for attorney general.

Almand emphasized that, as the only lawyer in the race, he was the only candidate qualified to take Melnick's seat on the House of Delegates' powerful Courts of Justice Committee.

Karydes, on the other hand, contended that "the General Assembly is already full of lawyers" and said she had a "broader and deeper background" in the issues confronting Arlington as a result of extensive involvement in school and community affairs.

County Democratic leaders privately backed Almand for the third seat because, as one spokesman put it, "we're happy with the delegation as it is now." Almand, he said, was seen slipping more readily into Melnick's shoes.

All four candidates said Arlington needs to win more autonomy from the General Assembly. Specifically they said the county should have authority beyond the property tas to raise revenue and should be permitted to decide whether it wants an elected rather than an appointed school board. Elected boards are illegal in Virginia.

The three Democrats seeking the nomination for the floater seat waged low-key campaigns and said they spent most of their time going door-to-door to introduce themselves to voters. Party officials called the race wide open since there was no incumbent running.

All three supported the proposed Equal Rights Amendment and said they would vote for it, but Montague added that he is not certain he would vote to discharge it from the committee where it has languished during recent sessions.

McCaskill was the strongest supporter of collective bargaining for public employees, which has been declared illegal by the state Supreme Court. Heinz also supported collective bargaining, but said a no-strike provision would be "politically essential." Montague said he is "open-minded" about it, but feared collective bargaining procedures could interrupt public services.