London — Is Britain still a weak link in the West's security system? Have the lessons learned in the Burgess-MacLean-Philby security scandals of the 1960s been steadily eroded by a national habit of carelessness in the keeping of secrets?
The questions are becoming insistent as United States officials continue to complain that Soviet intelligence has penetrated a top-secret communications center at Cheltenham.
This week the US defense secretary, Caspar Weinberger, said there had been a ''serious breach'' of security at Cheltenham. Whitehall officials are refusing to discuss the matter openly, but there is widespread talk of American anger that security arrangements at the communications center have been lax for months if not years.
Former employess at the center have spoken of clumsy security procedures. It is believed there has been a major tightening up of security at Cheltenham, but US sources say much secret information may already have been passed to the Russians by Geoffrey Arthur Prime, a Russian translator arrested in July on espionage charges.
Britons are asking themselves why lax security appears to be increasingly common. Earlier this year a man was able to enter Buckingham Palace and make his way to the Queen's bedroom. The incident led to a series of determined moves to improve security arrangements at the palace. But other incidents have followed.
This week two people penetrated the security screen at the houses of Parliament, climbed onto a repair scaffolding near Big Ben, and made a demonstration on behalf of a family member jailed for serious crimes.
The incident was particularly serious. In 1979 Irish terrorists placed a bomb in a car parked within the perimeter of Parliament. The car bomb killed Airey Neave, a close confidant of Prime Minister Margaret Thatcher.
The ease with which the demonstrators entered Parliament this time suggests that security arrangements tightened three years ago have been relaxed.
For Mrs. Thatcher the new rash of security lapses is deeply embarrassing. She is answerable to Parliament on security matters.
Sources close to 10 Downing Street say the prime minister has ordered a major review of security. Officials note that Britain's experience of spy scandals in the past makes it more than ever necessary for current security arrangements to be effective.
Part of the reason for security lapses is the reluctance of Britons to submit to seemingly humdrum security precautions. At the Cheltenham Center, it has been alleged, identity cards were out of date, and there was a backlog in ''positive vetting'' of staff.
There is also a widespread tendency in Britain to let people known to security officers pass through ''on the nod'' rather than insist on correct procedures.
At the time the Queen's bedroom was entered, one key security official was out walking the royal corgies - an instance of informality and a general air of relaxation.
The penetration of Parliament occurred without alarm bells sounding. Scotland Yard is conducting an investigation.
Meanwhile, Mrs. Thatcher is expected to make a statement on the Cheltenham security leaks as soon as an investigation is complete.