Those waiting to see which side Justice Sandra D. O'Connor would take in the Supreme Court's "law and order" battles got their first clue yesterday when she joined Justice William H. Rehnquist and Chief Justice Warren E. Burger in a conservative statement on the rights of defendants.

In her first substantive action, O'Connor joined in protesting the court's refusal to review a lower court ruling from Alabama. J. L. Stringer, ex-mayor of Hobson City, had been convicted of cashing someone else's city paycheck. During the probe, a prosecutor had telephoned Stringer to ask for some city records. In the conversation, Stringer admitted he had signed someone else's name on the back of a check.

The conversation helped convict Stringer in state court, and the conviction was upheld by the high court of Alabama. But a federal judge later reversed, on grounds that the conversation was inadmissible at the trial because Stringer's lawyer wasn't present during the phone call.

The court declined to review that ruling. Rehnquist, joined by Burger and O'Connor, dissented. In addition to challenging the lower federal court's understanding of the right to counsel, the dissent said: "It is scarcely surprising that fewer and fewer capable lawyers can be found to serve on state benches when they may find their considered decisions overturned by the ruling of a single federal district judge on grounds as tenuous as these."