Navy Secretary James H. Webb Jr., breaking a two-month silence on his opinions about U.S. escort of reflagged Kuwaiti tankers in the Persian Gulf, criticized other nations for not providing more military assistance there.

"What I would like to see is other countries who are benefiting from what we have done . . . living up to their responsibilities so we can downsize our presence," Webb said in a interview on the "MacNeil/Lehrer NewsHour" yesterday.

Webb's remarks differed sharply from a statement earlier in the day by Defense Secretary Caspar W. Weinberger, who said in an ABC television interview, "We're getting a lot of help from Europe and from other states."

Webb refused to discuss the contents of a memorandum he sent to Weinberger in July questioning the naval buildup in the gulf. He described the memo, reported by The Miami Herald, as "a classified think-piece" that may not necessarily describe the changing gulf situation today.

"If I could not support a policy that puts people in danger, I would leave my job," Webb said.

In a related issue, the Defense Department has told top congressional leaders that the Persian Gulf operation will cost $15 million to $20 million per month in extra operating costs "if the current level of activity is maintained."

Deputy Secretary of Defense William H. Taft IV said the cost of escorting the reflagged Kuwaiti tankers is being absorbed by the Navy, which is deferring maintenance of ships and equipment. He said that by the end of September, the Navy's operating costs will be $70 million higher than they would have been were there no escorting missions.

Taft wrote Congress that the costs of the gulf operations justify undoing cuts by congressional committees in the Navy's fiscal 1988 budget requests for operations and maintenance. The House's version of the defense authorization bill would slice $1.9 billion from the Navy's requested $25.6 billion operations budget while the Senate bill would delete $564 million.

Even if Congress eliminates the cuts, the Defense Department may ask for additional funds to pay for the gulf operations, Pentagon spokesman Robert B. Sims said yesterday.

The Pentagon yesterday released copies of Taft's letter, which was detailed in Saturday's editions of The Washington Post.