Some 25,000 more Maryland residents will go on welfare if various cutbacks proposed by the Reagan administration are approved, the Maryland congressional delegation was told yesterday by Kalman R. (Buzzy) Hettleman, state secretary of human resources.

Hettleman was one of six members of Gov. Harry R. Hughes' cabinet who went to Capitol Hill to outline the effect of protected cuts to Maryland's two senators and eight House members. They were told the cost of the additional welfare recipients would be $25 million a year, divided between the state and federal government.

He conceded his figures were estimates, but said: "Everyone is guessing, from [budget director David A.] Stockman on down," Hettleman called his figures "a very modest projection."

In addition to increasing the current welfare roll of 218,000 by about 10 percent, Hettleman said nearly all of the new recipients would be eligible for food stamps, which would further erode savings sought by the federal government. He said most of the extra welfare recipients would be children whose parents would either lose jobs now funded by federal programs or give up marginal jobs because day care help would be eliminated.

Hettleman said he and his colleagues came to Washington "to assist the delegation in understanding the magnitute and implications" of the budget cutting.

Sen. Charles McC. Mathias presided. Rep. Clarence D. Long (D-Baltimore) was the only delegation member who did not attend. Hettleman said his presentation was "very well received. Even though some minds are completely made up, all were starved for facts."

Also attending from Annapolis were the secretaries of transportation, health and natural resources, the superintendent of schools and commissioner for higher education.