President Reagan nominated deputy White House press secretary J. Daniel Howard yesterday as assistant secretary of defense for public affairs. He replaces Fred S. Hoffman, spokesman for former defense chief Caspar W. Weinberger. Hoffman has not announced his plans.

"It's been fun, kids," Howard told White House reporters in his farewell. "It's a tough beat."

Another former White House press aide, C. Anson Franklin, was nominated yesterday for the post of assistant secretary of energy for congressional and public affairs.

Jennefer Hirshberg, assistant director of the Office of Management and Budget for communications and public liaison, will be joining Ogilvy & Mather Public Relations next month. She'll be a senior vice president; former Carter press secretary Jody Powell heads the office here. Learning the Ropes . . .

Rep. Joseph P. Kennedy II (D-Mass.) remarked on what he has learned as a freshman representative: "I thought there would be great debates back and forth here. I really did. But there are no debates."

He told The Boston Globe that the House takes up too much time in parliamentary procedures. "The lows are the personal side, and that is just horrible . . . . I have been home one night in two weeks, and that is really hard." Common Appeal . . .

Common Cause, viewed widely as a catalyst for change, has come out against overhauling the Hatch Act.

In a letter to senators, Common Cause President Fred Wertheimer said that "efforts to abandon the fundamental concept of an unpoliticized civil service are dangerous and unwise . . . . Repeal of the Hatch Act's basic protections would increase the potential for building a powerful political operation based on the use of government workers and erase the narrow line between lawful administration discretion and political favoritism."

The House voted to revise the act last month. Senate hearings are expected early next year.