BRUSSELS (Reuters) - The European Commission proposed tightening rules on lobbying on Wednesday to oblige more EU officials, legislators and diplomats to restrict access only to lobbyists who register and abide by a code of conduct.

The proposals, to be considered by the European Parliament and Council of member states, were in the works long before the EU executive faced questions over its former president's move to Goldman Sachs in July and an ex-commissioner's failure to disclose an offshore directorship.

The Commission is battling to regain public credibility for the European Union in the face of a rising in nationalist opposition exemplified by Britain's vote to leave the bloc in June.

Its plan will notably make registration mandatory for lobbyists seeking access to policy-makers and extend the system beyond the Commission to the Council and Parliament.

"We must be more open in everything we do," said First Vice President Frans Timmermans. "Citizens have the right to know who tries to influence EU law-making. We propose a simple rule: no meeting with decision-makers without prior registration.

"Through the (Transparency) Register, the public will see who is lobbying, who they represent and how much they spend."

Some 10,000 people are registered already, a figure that has increased sharply since the present Commission under President Jean-Claude Juncker took office two years ago and denied access to meetings with senior officials to anyone not on the register.

While the Commission proposes legislation, interest groups can push to block or amend it by lobbying lawmakers or the governments and diplomats from the EU member states. The new proposal would expand oversight into those institutions.

But Daniel Freund of watchdog Transparency International said the Commission's plan did not go far enough: "After the Kroes and Barroso scandals, the Commission had the chance to prove it is committed to more transparency and better ethics," he said. "Instead they’ve come up with timid, cosmetic changes."

Timmermans declined to comment during a news conference on outstanding ethics inquiries into former Commission president Jose Manuel Barroso and former antitrust and digital commissioner Neelie Kroes.

Barroso caused outcry by joining Goldman Sachs after the Brexit vote in a move his successor Jean-Claude Juncker said was unwise, if not in breach of the code of conduct. Kroes was identified in leaked Bahamas documents as having a role in an offshore business which she had failed to declare to the EU.

(Reporting by Alastair Macdonald; editing by Andrew Roche)