When Anne Arundel County Executive James Lighthizer returned from an out-of-town trip last Sunday, one of the first things he did was place a call to Baltimore Mayor William Donald Schaefer's gubernatorial campaign officials.

Lighthizer, a staunch Schaefer supporter, was anxious to hear an explanation of the mayor's widely publicized comments indicating that he favors easing a key feature of the Chesapeake Bay critical areas program designed to protect waterfront areas from overdevelopment.

Lighthizer was not the only Schaefer ally to be brought up short by the mayor's remarks last week on an issue that is akin to motherhood in Maryland. Schaefer's statements on the critical areas program, which is not even in place yet, and the state's rockfish ban, which he said could be lifted "in a couple of years," continue to reverberate through Maryland political circles.

They have delighted partisans of his opponent, Attorney General Stephen H. Sachs; momentarily confounded some of the mayor's own supporters, and been studied closely by some insiders who are still neutral in the governor's race.

For the mayor, the early favorite to win the Democratic nomination, last Friday's cavalier comments represent, at best, a momentary gaffe and at worst a significant stumble that could begin to erode his front-runner status.

In an appearance in Montgomery County, the mayor said that the one-house-per-20-acres provision in the Chesapeake regulations should be amended in "a year or 18 months" -- when the criteria will barely have been implemented by local jurisdictions.

Schaefer's campaign aides have succeeded in convincing supporters such as Lighthizer that the mayor is still fully committed to the bay cleanup and that his comments simply reflected a desire to reexamine the critical areas land-use criteria at some point in the future. "I have no trouble with a periodic reexamination," said Lighthizer, who credits Schaefer with helping get the critical areas program through the General Assembly this year.

But even Schaefer's supporters concede that the mayor could be hurt politically if he fails to extinguish the issue with a fuller public explanation.

Already, the critical areas issue appears to be having a subtle effect on Schaefer's choice of a running mate. Some supporters are renewing pressure on the mayor to select as his lieutenant governor candidate Del. Nancy K. Kopp, a liberal Montgomery County legislator, rather than Del. R. Clayton Mitchell Jr., a moderate from Kent County on the Eastern Shore who heads the House Appropriations Committee.

Combined with Schaefer's earlier comments waffling on his commitment to gun control and endorsing a limited return of slot machines to the Eastern Shore, the critical areas statement has given Kopp's supporters new ammunition to derail the selection of Mitchell, which recently had seemed a foregone conclusion.

Last Sunday night, as Schaefer attended a fund-raiser for state Sen. Thomas P. O'Reilly (D-Prince George's), leaders of the county's Democratic organization pressed the mayor with renewed zeal to put Kopp on his ticket. The arguments, presented in separate private conversations by Rep. Steny H. Hoyer (D-Md.) and state Sen. Thomas V. Mike Miller (D-Prince George's), were that Kopp, unlike Mitchell, would expand the mayor's appeal among women and in terms of geography, religion and philosophy.

Among the arguments made by Kopp's supporters is that the selection of Mitchell would appear to be one more example of a tilt toward conservative Eastern Shore interests whose muscle in a statewide campaign is negligible. Kopp, on the other hand, would widen the circle, since she is from the Washington area, is Jewish and liberal and is respected among educators, a potent combination that goes to the heart of Sachs' strongest constituencies.

"Clay Mitchell is a nice guy, but he doesn't add a single vote," said one Democratic officeholder who is eager for Schaefer to pick Kopp. "We all recognize the election is going to get closer, closer, closer. If Schaefer picks a woman . . . we can go to the beach for the summer."

The effect, if any, of the mayor's Chesapeake Bay comments on his choice of a running mate may ultimately be less important than their impact on his overall candidacy. If nothing else, said some of the mayor's supporters, Schaefer's indiscretion reveals a weakness in his campaign apparatus as well as the hazards of being a half-fledged candidate unprotected by detailed position papers.

"I think it was a mistake, I think he'll have to backtrack," said state Sen. Laurence Levitan (D-Montgomery). Levitan was one of several Montgomery County legislators who sang Schaefer's praises at a Gaithersburg luncheon last Friday only minutes after the mayor had talked to reporters about his views on critical areas. All the lawmakers at the gathering had supported the critical areas legislation those lawmakers supported.

"What he said is something that I don't disagree with," said Levitan, "except it's premature."

Levitan and other Schaefer supporters agree with campaign manager Mark Wasserman that the mayor was guilty only of clumsily expressing his position on the bay, whose cleanup they say he has long supported.

"The mayor's view," said Wasserman, "is that no law is so rigid or inflexible that it doesn't deserve reevaluation along the way." Schaefer's meaning, said Wasserman, was that a requirement limiting development to one house per 20 acres in some areas along the bay is sound for now but should be looked at again "when we have some experience under our belt."

The mayor's opponents see the comments in a different light. Stanton J. Gildenhorn, one of Sachs' Montgomery County campaign coordinators, said the mayor's positions on slot machines, gun control and the bay are eroding his support in the Washington area. "The Schaefer image is being tarnished on a daily basis in Montgomery County," said Gildenhorn. "He appeared to be a liberal, progressive mayor of a large, thriving American city, but he is turning out to be a conservative Reaganite."

Some of Montgomery County's uncommitted politicians are also watching with interest as Schaefer's positions on statewide issues trickle out.

Del. Donald B. Robertson (D-Montgomery), the House majority leader, who is neutral in the governor's race, said, "There is concern about the mayor's statement on critical areas . . . . He's spoken out on three issues -- guns, slots and critical areas -- and I don't think he's helped himself." But Robertson cautioned that he would have to see the campaign "play out a little" before choosing sides.

Schaefer supporters are hoping that the mayor will be able to put the critical areas issue behind him by more fully explaining his views.

Said Prince George's County Executive Parris Glendening, a member of the critical areas commission who has privately told associates he supports the mayor: "Maybe after he has some longer discussions with staff and takes a broader view he will be supportive. I don't expect every candidate to be in complete agreement with all his supporters' views, but I feel very strongly on this and I hope he looks at it very closely."