WASHINGTON (AP) _ David A. Zegeer, citing homesickness, resigned Monday as the Reagan administration's top mine safety regulator.

Zegeer, a mining engineer and former coal company executive, said he made the decision to step down as assistant secretary of labor for mine safety and health over the Thanksgiving holidays while visiting his wife at their home in Lexington, Ky.

''I'm getting to the age where I miss by family, my fireplace and Kentucky basketball,'' Zegeer, 64, said in a telephone interview. ''I hated getting on that plane coming back up here ... and realized that, if I didn't make a move now, I'd be here another two years.''

Labor Department officials voiced surprised at the announcement, saying the resignation, effective Dec. 31, had not been sought by Secretary William Brock or others in the Reagan administration.

No replacement has been picked, said Don Smyth, a department spokesman.

During Zegeer's three-year tenure as head of the government's Mine Safety and Health Administration, the agency frequently was criticized by the United Mine Workers union and the mining industry, occasionally for the same reason.

Both the American Mining Congress and the UMW on occasion accused MSHA officials of devoting too much inspection attention to large mines while allowing small coal operators to employ less stringent health and safety measures.

The industry also vehemently opposed regulations developed during Zegeer's tenure that would increase by several-fold what MSHA charges for testing the products of mining equipment manufacturers.

The regulations were part of a Reagan administration initiative to substitute user fees for taxpayer dollars in paying for several federal programs.

''We haven't always agreed with him, but, on balance, we think David Zegeer has done a good job,'' Jack Knebel, the American Mining Conference's president, said Monday.

Knebel, however, expressed fear that a series of proposed MSHA regulations generally supported by the industry on topics such as roof bolts, mine ventilation and the use of explosives might get sidetracked with Zegeer's resignation.

''We don't like to see a hiatus, particularly with just two years left in this administration,'' Knebel said. ''Inevitably, it's going to take some time to get a new person confirmed and get the ball rolling again.''

MSHA, along with the Occupational Safety and Health Administration, was one of the few agencies that escaped budget cuts this year. Zegeer said the agency will add 130 inspectors by Jan. 31 and is ''shooting for'' an inspection force of 1,201 by the end of fiscal 1987 next Sept. 30.

As for criticism aimed at MSHA, Zegeer said he was surprised he did not get more.

''That's just part of the Washington scene,'' he said. ''If a guy is thin- skinned about that kind of thing, he better not come up here in the first place.''

A native of Charleston, W.Va., Zegeer was a mining consultant before he sucecded Ford B. Ford as head of the mine safety agency in November 1983. A member of a National Academy of Sciences committee that wrote a report on underground mine safety in 1982, he had retired in 1977 as manager of mines for Bethlehem Steel Co.'s coal operations in eastern Kentucky.