U.S. Brig. Gen. James L. Dozier said today that he spent all 42 days of his captivity in the hands of the Red Brigades chained by one wrist and an ankle to a cot inside a small tent.

In his first full press conference since he was freed by Italian anti-terrorist police last Thursday, Dozier suggested that the fiercest confrontation with his captors came not over any attempts on their part to extract military secrets from him, but rather over the kind and volume of music to which he was forced to listen.

The 50-year-old general portrayed his captors as being somewhat amateurish. That picture contrasted sharply with the brigades' reputation for political sophistication and military precision.

It also clouded speculation here that the motive for Dozier's kidnaping was either to try to extract military secrets from him or was part of a plan to exploit the emerging antinuclear movement here.

Dozier, 50, speaking to the press in Vicenza before flying to Rome for meetings with Italian President Sandro Pertini and Prime Minister Giovanni Spadolini, said his captors made no serious effort to pry military secrets from him and their inability to speak English limited their interrogation efforts. When they realized his Italian was not fluent, they brought him an Italian-English dictionary, Dozier said.

While the general described the men and women who held him prisoner as "smart, well-organized criminals," he said they did not appear to be members of a military organization.

His worst problems during captivity were boredom and lack of exercise, he said, but he was not mistreated and was adequately fed.

He said he was forced to listen to eight or nine hours of loud, hard-rock music through earphones to block out any tell-tale noises that could reveal his whereabouts.

After he argued with his captors, who usually numbered four, they substituted waltzes and Gershwin and turned down the volume, Dozier said.

Past kidnapings by the Red Brigades were much more skillfully handled. Their management of the 1978 kidnaping of former prime minister Aldo Moro, whose presumed prison was located only last weekend, enabled them to keep this country in terror for 54 days.

When they kidnaped Rome magistrate Giovani d'Urso in December 1980, the brigades skillfully used the press to focus attention on Italy's overcrowded prisons.

During the kidnaping last spring of Christian Democratic politician Ciro Cirillo of Naples, the Red Brigades were at least partially successful in exploiting the economic and social frustrations in southern Italy after the earthquake disaster there in November 1980.

Several explanations are offered for the terrorists' apparent decline in expertise, a decline that may have helped police free Dozier and thus deal the brigades what authorities believe is a crippling, although probably not final, blow.

First, with the majority of veteran Red Brigades in jail, those still on the loose are increasingly forced to rely on the help of young or untrained terrorists.

In the past, for example, the Red Brigades would never have had anything to do with drug addicts such as 22-year-old Paolo Galati from Verona who, police now confirm, was the person who revealed Dozier's place of captivity--an apartment above a grocery store in Padua.

Another reason is that an overall weakening of support for the brigades in Italian left-wing circles has made it harder for them to find sophisticated theoreticians to guide them. Moreover, the cumulative effect of past police operations has cut sharply into a once-powerful organization that is now internally divided.

Antiterrorist experts here say the arrest in early January of Giovanni Senzani may have been crucial in freeing Dozier. Although the English-speaking Senzani, 39, and the Padua group reportedly were rivals, the latter may have been depending on Senzani--the mastermind of several past kidnapings. The ex-professor at Florence University was accused of being a contact with Dozier's kidnapers.

Today, Rome Magistrate Francesco Amato used new information gleaned from recent police work to issue 260 new arrest warrants for armed insurrection in crimes that go back over a decade.

Dozier, who leaves Wednesday for Washington where he is to take part in a prayer breakfast with President Reagan, said his captors did not appear to have international connections.

"They gave me no indication of outside support whatsoever and assured me they were Italian communists," he said.

The general said he was embarrassed because he failed to heed warnings to take security precautions against kidnaping.