Sen. Lowell P. Weicker Jr. (R-Conn.) said yesterday that General Dynamics Corp. threw a fund-raising dinner for him in 1981 and then charged it to the Navy without his knowledge.

Weicker demanded yesterday that General Dynamics send him a letter of apology and he alerted the general counsel of the Navy to its contents.

This unusual argument between a senator and one of the biggest employers in his state adds to the controversy over the financial practices of General Dynamics and its Electric Boat Division in Groton, Conn. A federal grand jury is investigating allegations of fraud by Electric Boat on its submarine building program, and the Pentagon's Defense Contract Audit Agency is challenging some bills General Dynamics sent to the government.

The Weicker dinner was held Nov. 11, 1981 and was hosted by P. Takis Veliotis, then general manager of Electric Boat. Two days later Veliotis wrote Weicker:

"Dear Lowell: I am tremendously appreciative that you took time out of your very hectic schedule to join us Wednesday night. As I mentioned to you when you arrived, I am writing to each person that attended and am urging that they join me in financially supporting you in your campaign efforts . . . . "

When Weicker learned yesterday from the ABC "20/20" television program that General Dynamics had sent a bill of about $1,000 to the Navy for expenses for his dinner, he demanded an apology from the corporation. Ernest J. LeFevre, General Dynamics vice president for government relations, sent a hand-carried letter to Weicker yesterday, which stated:

"As you know, this dinner was not a political fund-raiser but was organized as a private dinner party for honored guests in conjunction with the commissioning of U.S.S. Ohio Trident submarine . . . . We have talked with some of those who attended," LeFevre continued, ". . . and all have confirmed that there was no solicitation for political funds either before, during or after the dinner."

Weicker, according to his aides, was furious when he compared the LeFevre letter to the one from Veliotis in his office file. He sent both letters to Walter T. Skallerup Jr., Navy general counsel, with a covering letter that said:

"The General Dynamics Corp. hosted a dinner on my behalf on November 11, 1981. It was clearly a fund-raiser for my 1982 campaign. I have been advised by your office that General Dynamics charged the Navy for expenses associated with this dinner and that those were subsequently paid by the Navy. I was further advised that a Defense Contract Audit Agency report has noted and questioned those payments." Weicker added that he was sending along LeFevre's "misleading letter of apology" along with Veliotis' letter to use "as you deem appropriate."