Israeli authorities are investigating allegations that former Foreign Minister Abba Eban illegally kept tens of thousands of dollars in bank accounts in the United States, a Finance Ministry spokesman said today.

Eban, 62, said there is "absolutely no truth in the suspicions."

The director of the ministry's foreign-currency department, Dov Kantorowitz, said an inquiry into Eban's affairs had been under way for a week, since the government received an anonymous tip that Eban held two accounts in New York City. Included was a photostat copy of a bank statement.

The investigation follows Israeli Prime Minister Yitzhak Rabin's leave of absence and his withdrawal from the May 17 elections because of illegal bank accounts he and his wife had held in Washington for four years.

Mrs. Rabin was fined nearly $27,000 after pleading guilty to charges that she held two illegal bank accounts.

Rabin, who was fined $1,600 for his involvement, has since taken a leave of absence, allowing Defense Minister Shimon Peres to assume many of his duties.

Kantorowitz said the sums involved in the Eban case were "a good bit more than the $21,000 held by the Rabins."

It was learned that the investigation involves an account opened in the Israeli-owned Bank Leumi in New York a number of years ago with the permission of the Israeli controller of foreign currency in the Ministry of Finance. The account was use for depositing U.S. royalties from Eban's books and for payment of related expenses.

According to one report, the regulations for such accounts were revised two years ago. The issue is whether Eban's account violates the new regulations.

Eban called the charges a "fabrication" and said that his New York account was handled by Bank Leumi in accordance with government regulations.

A Radio Israel report said that Eban had "apparently commited a technical breach of treasury regulations."

Israeli law prohibits foreign bank accounts without specific government authorization. Violators are liable to a maximum jail term of three years and a fine up to three times the amount of their illegal holdings.

Ironically, Eban's political fortunes rost two weeks ago when Peres replaced Rabin as the Labor Party leader in the May elections. Eban had supported Peres over Rabin at the party's February convention.

If the Labor Party wins the general elections, Eban had been considered likely to receive a Cabinet seat, possibly foreign minister, the position he held from 1966 to 1974.